I know it's they're oversize. A quick google pulls up clamp on bosses at sizes up to 1.5". I'm not near my cannondale frame at the moment, but that seems close to where my memory has a typical cannondale DT.

I'm just hesitant to drill anything, especially because typical DT boss location is right around where you'd hit a taper from the butt to the thinner wall in the tubing. If the frame is even butted. Just seems like a lot of potential for issue especially because I don't see anything other than a handheld drill making the hole.

What frame is it OP?