I've tried to use the mouse on the left side with little sucess. I did use it once successfully though in a Tomb Raider game when Lora was on a motorcycle and I needed to shoot continously while using the arrow keys to drive.
Wow! You're more talented than I am! Shooting AND driving.
It took me awhile to get used to mousing with my left hand. But it's turned out good really since I can now use my right hand for those more intricate keyboard moves: forward, back, hit, access, jump, etc. Of course, with an adventure game, it's not such a big deal using a mouse, left or right hand, for me, because most of the time, movement is relaxed.