well if you're replacing the thermostat, then you could 'adjust' the old one (hammer and blunt instrument) to get clearance for the housing past - plus a little tweak of the pipe position upwards may do the trick.Well, the thermostat housing came away with barely a struggle - the problem is that it can't move enough to free the thermostat itself because of the bulk of the thermostat keeping it all lodged in place.
The thermostat shouldn't be very tall unless it was put in upsidedown!
[I've never actually done this... but it seems like a reasonable idea]