I sold these bikes for quite a few years, and the problem with smaller frames is (as you mentioned) there is no room for a bottle cage. I wouldencourage you not to try to do anything to alter the frame. First, you’ll absolutely void the warranty on the bike. Second, whenever a frame is drilled or compromised, it increases the possibility of cracks and frame failure. Here’s a pic of a steel frame I bought that had been drilled for hidden cables (at the factory). When I sanded the paint away for a refinish, I found cracks at the hole. I’m not saying that would happen with aluminum, but it’s a possibility. You’d be drilling through the thinnest part of the tube. I recommend looking for an alternative. Plus . . . you’ve got a nice bike!