So, to this end I got hold of a cheap tabletop hot wire scroll cutter and some blue styrofoam. The cutter is this one. Having used it only once, I hesitate to give it a full review, but it did what I expected and needed it to do!
After some sanding, I took two of the hills to use as a test and applied some Homebase emulsion (shade: "Village Green"), a layer of PVA and a generous scatter of Gaugemaster GM170 static grass. I'll apply some spray varnish when I'm certain everything is totally dry. I think I'm pretty happy with the result, and will finish the set.