That's a pity you can't fit those on a shelf, though.If you're doing a permanent display you could just build the footpath of the modulars onto the actual roads themselves. I've done it before for a temp display and you can kind just separate the ground floor off, and move all the tiles forward on the original base plate and move any others onto the footpath of the road baseplate. It does give you a little room to make some grungy alleyways inbetween buildings as well!
I wish someone would sell 16x32 roads (just road, without pavements) and 16x16 cross.