Getting our little Taipei branch office “official” here, and while we did find a good accountant, the service for them to provide an address has a ton of additional services we don’t need or want, (it’s a “business center” with full office services).
Looking around that seems to be the most common option though. Does anyone know where to find somebody providing only an address (for business registration), and perhaps a mail forward option without all the other bells and whistles? 
I think the term you’re looking for is a “virtual office”. Plenty of Google results even in English:
Right, but those are all business centers with a ton of other services rolled into their packages. I.e. we’re not looking for a virtual office, we’re really just looking for one thing - using the address as the “official” address of the branch office.
My wife’s family has plenty of addresses we could use, but mostly residential, and I’d just as soon not be quite that joined at the hip w/them. 
Eta - on closer look Premia has an address-only option that should be perfectly adequate, thanks! 