I am having the same problem having changed at least 4 switches doing away with the need for the cassette safety switch and just using one quite early on in the game.
I plan to try and put a push button in by drilling open the 1/2 "top of the turn and push spindle (inside the loo). Insert push button switch and then threading wire down tube to emerge near the bottom where I will drill a small hole in the bottom of the cylinder before it screws into the flush mechanism. then simply connect wires to the ones that originally went to microswitch.
Richard
May 2011