Hi Gandolf, I have confronted this problem in several ways. A popular solution would be to get a Cabelas kit. The cheaper one of the two they offer. I'v been using one for a couple years now to take to classes and the only weakness is that the cam lever itself is not hardened and peens over. It continues to be serviceable however. If it really fails, the lever itsesf can be replaced with a Thompson part. The pin that provides the pivot for the lever is a threaded piece.
Anyway, getting back on track, Remove the small metal base from inside the kit box and epoxy it into a larger box that you build.
The only requirement will be that your new box will have to have a depth of eaxctly 2 inches. Now the weight of your entire box will be your platform. Basically you'd just be making the Cabella's kit vise fit into a new, larger box.
Good luck.