I don't have an S80 so I don't know if you can see the solenoid lugs.
How to make a service socket if you don't have one didn't I already explain?
install a heavy wire =<14 gauge to the solenoid lug terminating in a female Molex pin (get one with an insulator since you cannot let this wire randomly touch ground anywhere. Secure it safely somewhere to keep it safe with a ty-wrap or tape. Then make a jumper to reach the battery, I suggest that you get a suitable alligator clamp to grab the + terminal of the battery and a small alligator clamp on the other end that can grab the shank of a small screwdriver that can be poked into the New Service socket to start the car.

Have the service socket several feet away from the battery, as Volvo does in the 850 since you will get some sparks when you do this, and you don't want sparks near a lead acid battery since there's a chance of explosion.

If you don't understand my posts, just print them and show to your mechanic.

Bill