***NOT A LAWYER***

But I will give my opinion. I do not see how you are going to get around that waiver. The bike shop is going to say the bike was in perfect working order when you left with it. You can not say it wasn't in perfect working order because you did not inspect it and bring it to their attention at the time of the rental. I feel really bad for you and wish you would not be responsible, but to me it seems that that waiver makes you responsible. Has their been any dialogue between the bike shop and yourself concerning the incident?