InstallAnywhere will pick up environment variables that are prepended with "IA_PATH_", this provides another solution to the one that pv has suggested. Whatever paths you use in your project, set them in your environment with 'IA_PATH_' prepended to ...
I had the same issues as you guys. I eventually just put the vms in a location where I had the diskspace to keep them and put soft links to the vms in the installer_vm directory.This is what I used: IALocation="${env.IA_HOME}" IAP...