Success!
Spike,
Just took the old unit out and it seems that you can remove the front switch panel from the electronics by undoing 6 small star-head screws (4 at top, 2 below). At first glance these screw positions seem to be the same as those on the as-new A3 climate unit I bought off ebay, which fits the A2 dash. Basically I should be able to take the A3 panel cover off, put it back on the A2 backpiece (thus keeping the old electronics as they were) and hey presto - new switches!
I'll keep you posted. If this works then it's the cheaper way to go as A3 climate units are more available than genuine A2 pieces.