Salamandrine 

Yep. That's the old school way to route bar ends and it does work. Nice.

I think if going with old school housing and old school friction shifters, this is a better choice. If the OP wants the housing wrapped all the way to the top, better to use modern slick cables and lined housing.

BTW, cables used with unlined housing would have had a very generous smear of grease. Pretty much as much as you can get on there. Grease is not optional. For some reason this seems to scare people today.

Anyhow, as far as friction, it all adds up. Lube, cable routing, rebuilding the shifters, filing and dressing the housing ends, ferrules.

Going to under BB routing as suggested could help too. If this bike has a clamp on RD stop, it'd be easy enough to shift that around to the bottom of the chainstay. I'd do the other stuff first though.