not got round to doing it, but I wondered about flooring the shed in a (maybe 2) layer of 17mm ply with some kind of anchor fixed with t-nuts (araldite to fill in the socket head bolt heads)
with the bike on top of the ply and anchored to it with as little slack as possible, the whole thing would be difficult to shift
mind you, I have no idea where you would source thick ply, t nuts and socket head bolts?