I don't think that would work. When I mounted all the ISOs without that, they all appeared but the game still wanted me to switch discs. I'll try it out though.
EDIT: that just consistently says insufficient system resources to mount the image
Is there anything I can use from within windows to make it think I'm swapping discs, maybe some function of sheepshaver or something to let me swap which ISOs are defined as storage?
I believe the error you are getting appears when the image being mounted is located in the shared ("Unix") volume. You must transfer the images into one of the SheepShaver volumes before they can be mounted inside SheepShaver. In my case, my boot disk was not large enough to hold multiple CD images, so I created another volume with SheepShaver, and stored the ISO images inside there.
While I cannot say it will fix your problem, I think you should try the Virtual CD/DVD Mounter again. It is an extremely useful tool. I have encountered several games that will not run from an ISO mounted as a volume in SheepShaver, but they do recognize virtual disks mounted using this utility.