Thanks for all the feedback. I tried picks, screwdriver, etc... without any result. i wasn't willing, however, to throw all my weight behind a screwdriver for fear of damaging something.

I needed the car running last night so i put the new injectors in using the 10mm heat shields that came with injectors. The car started and is running fine, much better than before actually. I'll probably research a bit more and maybe remove them again next weekend.