Interesting question. I once had a need to glue foam board to a
Tuperware lid. The Tuperware is a similar kind of plastic as used in
the Rix bracket. It can't be done as far as I can tell. I had a hard
time finding an adhesive that would firmly grip the plastic. Then,
any adhesive that would adhere to the lid ate right through the foam
board. I have not tried every glue out there, and since my experiment
new glues have hit the market, like Gorilla glue. So there may still
be some hope.
Note: You may not want to glue your switch machine to your foam. If
you don't mount it in the right spot the first time, or need to remove
it for any reason, it will take a chunk of layout with you. Why don't
you glue a piece of masonite to your foam and then screw mount your
switch machine to that? You will then be able to remove your
switchmacine. Elmer's carpenter glue works on blue foam as well as
hot melt. The Elmer's may take a few days to dry. But the hot melt
may loose it's grip over time.