Oh hellz yes!
I've trained AND raced with my right hand in a cast (bone behind the pinkie was broken after crashing over an insane suicidal groundhog) and with right hand and wrist in a cast after low-siding in an oily turn (one bone in the mess of bones that make up the wrist was busted...motor gently through the grease-mud, for there lurks the skid demon!).
You can do this!
I'm surprised the doc did not immobilize your middle finger by strapping it to the index finger and splinting the two of them together...but at least you can still flip off life's morons!
Go easy on the warp speed for the first week or so and try to plan your braking far enough ahead that you can drag just one brake. Yeah, that will kill you average speed, but at least you'll be out in the fresh air and getting a workout in.
Safety first...try a couple of fast, hard stops. If you can mange one, you'll be fine if you really have to lock it up. Good luck!