So the second prototype includes a big button which, through a sprung plunger, operates the switch with a steel rod.
It's an even more pleasing use of stock items than version 1. Again, it uses offcuts of 13mm MDF, but now with added delights: part of an old broom handle (the knob), a screw (the steel rod), a ballpoint pen spring, and a piece of a brass hinge (the plate which retains the spring). Oh, and a bit of glue.
It's going to be taken to Devon to be trialled next weekend. Fingers crossed.