Clearly the answer is to wheelie everywhere until it comes out
Non-comedy option - try rigging up a vacuum cleaner to some Tygon hose small enough to snake down in there. Test this out before routing it down the pipe to make sure it won't collapse the hose.
A telescoping magnetic pickup tool like the one pictured below would work. Even if it did stick to the inside of the pipe, you could still drag the nut up and out.
__________________ I just want to ride fast and bang hot chicks