Speedy recovery to you, Jo. Listen to the doc - seems like he's supportive of what you want to do, since you said he hasn't ruled it out. Good! There's hope, just be careful. Don't overdo!
I like RoadRaven's idea about the trainer...to keep your fitness. That way, if you do get the go-ahead from doc, you'll be ready.
I'm riding the cycling leg in a team relay triathlon on the 2nd, same day as your century. I'll keep you in my thoughts while I'm out there trying to rip my lungs out.
Take care!
-BikeMomma
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." --Albert Einstein