Bumper (Fender) repairs

[quk@sievers.com (Phil Payne)]

I smacked F600 JVJ into one of those annoying waist-high black posts that 
litter pub car parks.  Apart from some scuffs, damage seems to be limited to 
the rear bumper (fender).
 
All praise to the Audi gods.
 
I demounted it (four easy 10mm nuts in the boot (trunk)) and had a look.  The 
metal part is bent, and should be fairly easy to bend back.  The heavy (PVC?) 
cladding wiped clean and is undamaged.

However - to be able to bend the metal back, I had to separate the two.  There 
are six hex-head bolts screwed into captive (brass?) ferrules embedded in the 
PVC.  They were all corroded to hell - three came out OK, three just turned 
the ferrule inside the PVC. I drilled off the heads - bingo!
 
Now - reassembly.  What are my chances of removing the remainders of these 
screws?  Chemical treatment?  Looks like zinc-plated very mild steel in 
brass.  Drill and stud removers? Get the whole ferrule out and 'engineer' 
something to replace it? It's a 'blind' operation, because the other side of 
the PVC is the polished outer skin.  Drill through the defunct screw into the 
plastic and use an extra-long blind rivet?  Drill into the old screw and tap 
the hole?  Remember the ferrules turn - I'd have to locate them, perhaps by 
drilling through sideways?

Any ideas?  Engineering is scheduled for tomorrow evening.
 
All praise to our "new" 1985 Coupe GT, which has stepped into the breach to 
fetch and carry parts and family while the urq is laid up. 

--
 Phil Payne
 phil@sievers.com
 Committee Member, UK Audi [ur-]quattro Owners Club