ReadyBoost won't help much with RAM overcommit (paging). AFAIK, it only caches file read access, because Windows still has to be prepared for the device to be removed unexpectedly. As you can imagine, putting the pagefile on there would be a really bad idea.

Can you tweak the memory usage of the VMs down a bit? If you could shave 0.5Gb off two of them, you'd be back in-budget. Also, as far as the SAN simulator goes, you might get better performance if that I/O was backed by a physical disk or partition, rather than a VHD/VMDK file.