This is something that I've been thinking about too. Since getting my permit earlier this year, I still haven't worked out the details to carry when riding my bike. I always use a CamelBak, whether road / canal path riding or trail riding. I haven't carried in that mostly because I know it's not readily / easily accessible. Also, in the event that I ran into trouble while riding somewhere, and lost possession of my CamelBak or was injured, that would lead to a whole other pile of issues. Example; two years ago I took a spill and broke my wrist. Luckily my friend was with me and helped get me and my bike out of the woods. He loaded all my gear in my Jeep and drove me to the ER. I guess in a worst case scenario I could have locked it up in the glove box? I just don't like that option, especially with the location of some of the hospitals in Rochester.
I usually wear either MT Bike shorts, or Lycra bike shorts with loose cargo shorts over top with a loose-fitting shirt, and I haven't figured out a good way to carry yet. Maybe I'll look at something like the High Noon that Jeff suggested. The only thing though, is that I've had a few good crashes over the years, and I think that having my pistol holstered somehow on my body would hurt like a b!#$% if I were to fall directly on it. For now, I just keep a knife clipped to the waistband of my shorts.