There are 3 solutions to the problem. One is put a switch on the wall
near the sink, which is the most common. Another is buy one of the
batch type disposers that run when you put the lid on it. They are
usually used for homes where small kids are a concern, And the last
solution, I'm pretty sure I've seen a relay type gizmo that will turn
the disposal on. The settup has a push button that goes in a spare
hole in the sink, like where a soap dispenser would go. From the
button to the relay I think they use air to activate it, so for saety,
there is no electric going to the actual sink button.