Hi Derek
As far as I can recall every previous 1994-1999 850 / V70 I ever owned (about 6 in total, petrol and diesel) had a coat-hanger type pull cord attached to the motor with a handy finger-ring that was revealed upon removing that little bit of quarter carpet that gives access to the tail lamp bulbs. I often had the need to use it especially in winter when road grime got inside the flap and gunk up the locking pin if I was not diligent enough in regular washing.
If it makes a difference to working out which cars are "affected" by the omission of an emergency release, again as far as I can recall all those previous cars had fuel flaps with a bent metal tab on the trailing edge with a circular hole to accept a round pin from the locking motor. On this current 1997 car the fuel door has a black plastic clip with a square toothed peg that locks behind a square pin!........like this one;
https://www.youtube.com/watch?v=Bz6P4NuRXT0
......Its the kind of detail only serial Volvo beards would probably even notice!
Today, with the help of someone operating the door release button, I just managed to feel around inside the rear wing and find the plastic tab which would release the fuel door if pulled manually. It is EXTREMELY difficult to get at unless you have arms and hands the size of a 7 year old. I tried reaching in with my right hand but my elbow joint was unhelpfully in the wrong place up my arm, and I had to sort of stand to the right side of the car and reach around the tail lamp with my left hand – its that tight!
I don’t think the carpet/bulb aperture would be sufficient, you would definitely have to remove the whole side boot trim. Even if you're the kind of person who carries sockets and screwdrivers with you its still not a job to relish at midnight with an empty tank at a rainy petrol station (especially when the boot trim plastics are getting so fragile now after nearly 3 decades).
So, as I have yet to reassemble the freshly cleaned boot panels, in the next couple of days the fuel door motor is coming off and I’ll drill and fix a cord or wire to this as-yet unseen tab and loop it back to the tail lamp void, as Volvo should have done in the first place.
Interestingly it is very difficult to find anyone with exactly the same problem we have re: the fuel door on the myriad of forum threads on the net. Most replies just point to the wire pull cord most cars seem to have. Even the almighty Robert DIY hasn’t got a fix, his Youtube video in the subject uses an S70 as an example, which is sadly irrelevant. Only on the US Volvo Club site did I find ONE short thread where someone queried this; his description of reaching inside the wing to find the pull tab was funny and accurate – if you are not grimacing in pain you have not reached far enough!