I have an old set of suntour stem shifters and I've been thinking of what I can do with them. One idea that came to me was a suicide brake.
As you can see in the picture, I just attatched a seatpost where it would normally clamp on to the stem, I would then weld together the shift levers and also weld on a frame clamp.
With this I will be able to control two brake (one attached to each of the original levers), I remember seeing online a while ago about someone who had attatched both brakes on the back so that he could lock up the rear wheel.