I have a very simple solution (albeit for a folder at the moment but easily made for a full size bike) ....... Imagine a giant shower cap made from very lightweight ripstop nylon ... shaped like a bike (pretty much a rectangle with one long edge open with a hem and elastic. The whole thing pops over the bike, with wheels off and strapped to either side of the frame.
The other option that we have taken (but haven't yet needed to implement) is our "end of tour jobsworth on the train solution" - it's a sheet of non-woven fibre material (like a j-cloth) that garden places sell as weedproof membrane + a roll of tape and some cable ties. Cable tie wheels either side of the frame, wrap the whole lot with the sheet material, taping it up. Hey presto, a parcel to take on the train ... and open it and throw away the sheet (costs peanuts) on arrival at the destination. [And when we've been organised we've mailed the "bag" in a poly envelope to the last B&B on the tour route.
Rob