I have a spot weld drill 'kit' from Machinemart.
On the passenger side I used the drill to take out the welds, but the VW spot welds are larger than the drill bit. This resulted in a couple of small tears at the back of the runners.
On the driver's side I'm now using the mini-hole-saw supplied, to cut around the spot weld in the runners. Hopefully this will free the runners and then I'll scurf off the remaining centres.
I would rather not have to fill lots of holes in the shell!
The big issue is just how many spot welds VW used on these cars! I got most of the way down the driver's side inner runner and then realised there were STILL another seven welds to drill out.