so I might sacrifice an old front wheel and clamp the hub shell to the rack as a cheaper version of the (overpriced) dropout mounts.
FWIW - I have done this ^ before to tow 26in and 700c wheeled bikes behind me for short (ie: <5 mile) distances and it works acceptably for occasional use. As long as the hub is firmly attached tot he rack it's quite stable. I then just use toe clip straps to tie the (removed) front wheel of the bike to either the side fo the rack or the side of the towed bike.
I did toy with the idea of making a bolt on boom that was going to attach to the BOB Nutz trailer hitch mounts already on the ends of the axle of the towing bike, and triangulated up to also bolt to the rack, and then have the 'towing hub' basically suspended at roughly normal axle height a few inches behind the wheel of the tow bike, but haven't got round to making it yet...
My other idea was to bolt on of those front axle mounts into the base of my BOB trailer so that I could carry a bike upright in the BOB, or since I already have a rack fitted over the back wheel of the bob (for extra panniers) so was thinking I could mount it there. Either way would have one half of the bike 'in' the trailer and the other on the trailer rack.
EDIT - kind of like this but my Idea was to have one wheel removed and the bike entirely on the trailer so not adding another rolling wheel into the mix.