[Reckers]

I ran across a site where a guy cuts large foam for surfboards, etc. Same principle and can be adapted to several versions for large or small work for model railroad layout building. Anyway, here's the site:

http://www.instructables.com/id/Hot-wire-foam-cutter/

His framework looks pretty awkward, but then, he's cutting big sheets in long curves. Easily adapted, though, for a smaller hand-held or even a table-mounted large model to do a long, vertical straight or curved cuts: a whole tunnel wall or mountain slope in one pass.