There are lots of switches around that can be made compatible with the Ensemble, simply by using an off the shelf adaptor. Most assistive technology switches just plug straight in.
Whilst surfing the web today I came across these switches that are designed for people parachuting to use to trigger their cameras. There is a Bite Switch and a Tongue Switch. I expect both of these could be useful.
A UK reseller is here: The Jump Shop.
Let me know in the comments below if you get one.