Personally I kinda like Mickey Mouse
but if you don't have an original mechanism and want to add a washer it looks like it could be done with a vacuum operated electric switch added.
I've got a call in to my friend who is a manager at NAPA (don't worry he worked his way up from the parts counter) to see if he can find us a vacuum operated electric switch (normally open - vaccum closes the contacts to operate the electric pump). Keep your fingers crossed - maybe he will come up with something.
Thought I would search ebay for a vac switch. Found this (130273074789) and called my local Suzuki dealer to get more info because it looked like it may work. They couldn't match the part # exactly - said if I brought a pic in they would most likely be able find it - either in the book or a cycle mechanic would recognize it. Figured if it was a few bucks I would get one and see how and if it would work. I have the original vacuum washer motor so don't really need it. The guy at the parts counter said most of the small electrical parts like that were around $50 so needless to say - I won't be picking one up.
I'll keep looking.