Routing recessed brake cables on non-recessed drop bars
 

Back before grooved handlebars came out I know it was pretty standard fair - and the way I've always done it - to route recessed brake cables on the inside of the brake levers down along the lower front of the bars, but I've noticed a number of cyclists from the "classic" racing era ran their recessed brake cables to the OUTSIDE of the brake levers and then somewhere along the back - or lower back - of the handlebars. Has anyone ever tried this, and is it more or less comfortable on the hands to have the bulge of the brake cables there? What is best path for the cables to take under the bar tape when routing them this way? I really like the idea of grooved handlebars to eliminated most of the cable bulge under the bar tape issue, but when building a period correct racing bike from the day and age before grooved bars (and after recessed brake cables came out) it makes sense to use regular bars and have the cable bulge there.

I run mine on the bottom of the bar, I don’t even notice it when I’m riding.

I've never owned a bike with that routing, but I worked on and test-rode many when I was a bike mechanic. Generally, I would route cable in the most "natural" path, which was usually on front of the bars. New bikes often came with long,clear flexible covers to go over the cables and smooth the feel. I haven't seen those aftermarket.
One suggestion in setting them up; run cables and adjust brakes before securing cables to bars or taping bars. Forcefully apply brakes to fully seat cables and ferrules into where they belong. THEN adhesive tape cables to bars and handlebar tape over it. Remember you might need to stretch the tape little since the effective diameter of the bars is now bigger.. most tape barely gives you enough already!

I know this isn't the same but the Ergos have an option for the second cable to route toward the front or back of the bar.
Initially I routed to the front and recently re routed toward the back.
In both cases, the housing was located to rout to a bottom exit of the bar tape.
In terms of comfort, I don't notice either cable, shift or brake on the bar except when my hands are on the bend. Then the bar feels a bit "wider" due to the cable on either side of the bar. I really don't think too much about it as I usually ride on the hoods.

On mine, I put the cable along the front of the bars. As long as the cables are not directly under your palms, they should be fine. You can get an idea of how it will feel by taping the cable in different positions and trying it out before wrapping the bars.

I'm thinking the bar tape used when we had to try to do this in the most comfortable, best looking way (before grooved handlebars came about) must have been thinner than most of it is now because the thicker the bar tape the worst it looks, since the bulge gets exaggerated as the tape thickness grows. I always used Benotto tape on my racing bikes, which was starting to go out of style with the pros a few years after recessed brake cables made their debut. This tape didn't look too bad wrapped over brake cables, although you definitely knew they were there. But even the other tape used back then (whatever it was) seems like it looks better than what's available today. Except for a few companies - like Fizik - which still offer a thin 2mm thick tape, everything else readily available today (except cloth) is the thick 3mm EVA foam tape.

I’ve seen bars drilled for interior cable routing also. In fact, I think the bars that came on my de rosa are drilled. I don’t notice any extra flex from the holes, and they exit in the sleeve, but I couldn’t figure out how to get the hosing through, so I gave up and went around the front of the bars.

not sure how anyone else does it, but you could install the length of housing you need onto a steel cable. using a strong magnet, guide the free end of the cable through the bar to the sleeve opening and pull the cable through with needle nose. use the cable to pull the housing through. then, pull out the cable, install through shifter, and route through the housing

Not at the very bottom of the bar, but close. When my hands are on the top of the bars I like to feel the housing (underneath the tape) in the crevice of my first knuckle(s).

that's how i do it. it's kinda like a handle bar grip

Cinelli actually made some bars drilled this way from the factory. One was called the "TOP 64". They show up on eBay from time to time.

A bit of string and a hoover is the traditional method (for bars you need end plugs).