This is in my opinion a much better way of dealing with SD cards than my previous fix.

Instead of adding a momentary switch to fake the insertion of the card I have modified the ultralcd menu item:

Card Menu -> Refresh

to reinitialise the card providing that the SDCARDDETECT pin has been set to -1 in the pins.h file.  This requires one less switch on the front panel and the refresh menu item is in the most relevent place for a user who wishes to inert a card and then print from it.

It also means that the "Card inserted" messages do not bother the users of these card readers (they dont make sense for users without SCCARDDETECT)