I'm not in a position time-wise to help you with the IIfx board (hope Phreakout PM'ed you). However, I thought I'd mention that Digi-Key has the plastic battery holder for the 1/2AA battery. It's been a month or so since I looked it up but it was in the $2 neighborhood. Maybe $1.25, maybe $3... So if the board is repairable, the battery holder is available...
I also have a small supply of battery holders I found in my parts mound. So, if one is ordering capacitors from me (see thread in Trading Post) one can add a battery holder to the order for $2. One of these days I'll add that option to the actual posting over in Trading Post. But you're not a likely customer for my capacitors (unless you also have an SE/30 or such) because the IIfx's I've seen all have beautiful tantalum capacitors installed at the factory.
Jeff Walther