Ooooh, I know that feeling. After I got my knee 'scoped, I did almost exactly the same thing, but didn't get beyond sitting on the bike and realizing that The Knee was NOT going to bend enough to do a full revolution. I went back in the house almost in tears. Such a fine spring bike-able day, and it was going to waste. (insert favorite rant here)

When I whined at my PT, she suggested that I get on a stationary bike at the gym and just go around as far as possible, then go backwards. Don't try for a full revolution, just add a bit of motion at each stroke. Back and forth, back and forth, adding a bit at a time. It worked, though I'm sure I looked silly - and it did confuse the computer on the bike - I was pedaling not long afterwards.

I'd run this by my PT person, just in case, but it did work for me. (By worked, I mean it got be back on the bike and helped me hang on to my sanity)