This is a tough one... and may very well be worth tackling in the next season. Afterall, we're doing crutches and wheelchairs and I'll bet more people ride bikes than use those devices.
When I carry while I ride, I generally accept the compromise an have carried small framed revolver or subcompact pistol in a pocket holster inside my riding jacket.
If I'm not wearing a jacket, I have sometimes gone all the way to off-body carry in a magnetic tank bag, that I keep with me when I leave the bike.
Interestingly, although I generally think Open Carry is a bad idea, I have carried cross-draw openly when on long group rides in the west. These rides were usually through open country, off interstates and started and ended at camp sites in the national forest. This was probably the "best" way to carry in regard to speed of response, but came with its own compromises in regard to awareness or surroundings and limits to where we could go while riding.
-Rob