If it'd work without the rear bikes front wheel in the forks, that might work - OP said he doesn't want to take it apart though ...

Maybe use that X2cycle thing and somehow lock the bars/forks into place so that the rear bike becomes "rigid" for towing?

I've seen the fork mounted into holsters on the lead bike idea (attaching the rear bike by the front forks) but I can't help but thinking that'd raise the centre of gravity really high for that rear bike - it'd become tricky to manouevre - I had a fair amount of trouble with my setup above, and that was u-lock'd to the bike & bungee'd to my seatpost rack pretty damn tight.

Ghost riding/hand horse can be just hectic/crazy