Rugs, Carpets and Carpeting - Home made carpet stretcher

I've been considering making my own carpet strecther out of some wood and kayak foam. The trick is going to be reproducing those little grippers that bite in firmly yet move quickly to my next position.
Any ideas? I'd love to hear that someone already made a fairly successful one.

Yes. I know I could buy one but I'm only putting down a small room.

Yes. I know I could rent one, but I live in a remote area. (Really.) It would cost as much to return it quickly as it would to buy it so I'd be back to the "Why buy one for one small room" thing.

I'm just heading off the questions like from the local pros that were trying to sell me some service for this really small room. Business wise- I should hire them. They'd lose money in gas. I don't think they realize how far away we really are.

6 0r 8 penny nails for the head pins.

I had entertained that idea but thought it might be a little too crude. I'll post a picture of this thing when it's built.