Monkeyleg:
I bought my vest large enough to wear over my jacket. I carry a Colt Mustang Pocketlite in one of the inside pockets, in a simple Uncle Mike's pocket holster.
I know a vest over the jacket may sound a little strange - it did to me, until I took a road trip with 6 friends a few years ago into Milwaukee for Harley's 95th Anniversary bash. I found that, especially with gloves on, a vest inside my jacket made toll booth & gas stops a real hassle. I was constantly having to remove my gloves, unzip my jacket, fish for the ticket and/or money, etc. At stops, I held everyone else up. The others were wearing vests outside their jackets, with those chain link expanders across the front to hold them from flying in the breeze. I now carry a few $$ in bills & change in one of the outside pockets, with my driver's license & CCW permit in a small leather & clear plastic "license" holder inside the other outside pocket.
The vest is definetly big if worn over a t-shirt, and the arm holes which are usually big in a motorcycle vest to allow for reach will expose a shoulder holster.
I have been looking into carry holsters for my Ultra CDP that would be comfortable while riding. I am wondering about a cross-draw that sits almost horizontal on the belt - have you seen these? A typical vest of jacket would seem to hide it, & the holster wouldn't dig into the seat. I've never really been a fan of cross-draw belt carry, but it might work here.