Have had tedious success w/ hack saw blades slipped under the panels-
Long metal cutting blades in a Saws-All will work especially @ the
perimeter but sometimes will grab the fastener & bang into the panel &
dent it.

Have grabbed the hacksaw blades with Vise-Grips & sawn away,
Have wrapped the blades w/ duct tape, have screwed together a handle for
the blade by kerfing a
dowel .

For interior field fasteners have welded hacksaw blade to a 2ft pc of
steel strapping & slipped it in & sawn away.

To start opening up the field I've punched the heads of the screws &
just hand drilled-
Don't know what size the fasteners are- but I would suggest that you use
a drill bit almost as large as the nail head-
If you are really bent on making up a tool for drilling-
suggest that you could fairly easily modify a vix-bit-
Silver solder a cup/ sleeve the size of the fastener head to it.

Of course then I don't talk Kiwi & maybe you don't know what a SawsAll,
Duct Tape & Vix-Bits are.

Drew Diaz ;{ )