You could build a PVC bike rack custom for the van. It's pretty inexpensive and you could build it in an hour or so if you are handy.
http://www.gonebowlin.com/camping/br.htm
http://www.utahmountainbiking.com/bikerack/makerack.htm
http://warp.byu.edu/TruckBikeRack
I stole the following image from another BF post: