I was actually thinking that these may be a good building block for building "static" terrain boards and/or modular ones. Maybe this route would be too much work, but...
If you cut the various hexes, position them into place - do some extra contouring etc. and then use Captain Blood's GOOP™ on them to hide all the lines you would end up with a nice rolling effect with the added benefit that you would know (because he already worked it out in prototyping) that figures won't fall over.
Again, it may be WAY too much work compared to just cutting down a full 2' x 4' piece of foam - but then again it may be worth it? I'll have to see come the spring when they show up.