Jon Goodman (interslice on eBay) sells an adapter which takes the 675 hearing aid battery and exactly mimics the shape and size of the 675 housing. This is an advantage over the 0-ring approach for cameras that have unusual locations for the contacts.

Jon is really helpful - his main claims to fame are his camera light seal kits.

No connection, just a satisfied customer, etc., etc.

EDIT: The hearing aid batteries use exactly the same battery technology as the Wein cells. Jon's adapter or the o-ring approach give you what is essentially a Wein cell with interchangeable very cheap hearing batteries. They give relatively short life, but it's easy to find them and a dozen are often less than one single silver oxide cell.