When I went to my VTX rally in Denver, CO I started taking pics on the fly like that. My camera was a smaller Sony Cybershot but I hung it from the strap over my neck like normal. I would just work it all left handed and hold it up to take shots. Granted only about 30% of them came out decent and you have to be real careful not to put too much attention on the camera

but it works... here's a couple I took (wish my camera was as good as his)...
I thought this one was cool...
over the shoulder...
My problem was having the windshield on the bike then, I had to raise the camera way up to clear it but it let me get some good scenery shots as I was riding that I wouldn't have other wise. I was riding 3-400+ miles/day all 4 days I was out there so not a lot of stops for picture taking