I ride a bagger Harley and when I first got it, I experimented with different ways to carry concealed and was concerned with A.) losing the gun, and B.) accessibility. With regards to (A.) I decided I needed a holster with a retention device. With regards to (B.) I needed to be able to get to my gun, if ever needed, with as much ease as possible.
After some trial and error methods, I was most comfortable with an Army Surplus Helicopter Pilot's Holster. I can carry a large frame semi-auto and the holster rides across my front lower left chest area. The gun (and holster) are secure, I don't have to worry about losing the gun because it vibrated out of position and a simple pull down of the jacket zipper allows easy access to the snap on the holster and quick pull-out of the firearm.
.45Gunner, sounds like your concerns were basically the same as mine. It seems like your solution would work well when you are out just for a ride. When the time of the year allows it, and I don't need more (i.e. no passengers or lots of junk to transport), I like to use my motorcycle as transportation as well as recreation. What do you do when you are using the bike to get somewhere and you get to your destination? It seems similar in concept to a shoulder holster, why did you choose this over a shoulder rig?
From the bulk of the responses, it sounds like a shoulder holster with a thumb break may be something I should consider. It would be a very different draw than my usual methods, but it would be very secure, somewhat accessible, very concealable while on the bike, and would still conceal well once I got to my destination so long as I kept my riding jacket on.