Front Grille/Bumper securing screw(s)

[rkidscd001]

I was going to fit my new debadged black front grille this morning, but I stumbled across a problem.

The securing screw on the top right came out with no problems, but the left hand side just keeps spinning.

I can see down the side of the bumper inbetween the headlight and the bumper, so I can see whats happening. The screw goes down through a threaded securing lug that serves 2 purposes, it holds the front grille and the front bumper in. The thing is, it seems that the thread is either seized or corroded, so when I turn the torx headed screw, it just spins the whole securing lug.

I have doused it in GT85 and just left it, but I think I need to get something in there to hold the lug while I undo the screw.

Any ideas of how I can access the back/underside of it to do this? Am I going to have to remove the headlight?