Took the son for a haircut this weekend, and dropped over to Campus Cyclery for a gander. He's about 4'11" too, and complaining he can't keep up with me. Of course, some of it is motor too, but he is not buying it.

Anyway, this is the same dealer that had Felt F24's, but he was sold out. Instead, he plopped the kid on one of these, and he fit like the bike was custom made for him. FWIW, it was the 40cm frame size, and had 650c wheels. Sadly, it's too pricey, but might be something else to keep your eyes peeled for.

There also seem to have been an awful lot of 650c tri-bikes made, although that may not be the geometry you are looking for.