Thank you all for some intelligent advice!
I did manage to twist one of the rack ears so the stuck screw moved a bit, then I
tried with a screwdriver of the correct size and the last screw was off! (I've certainly learnt a
lesson to always use right size driver..)
So now I've open it up and removed the top to get a peek of the back side of the
neutrik XLR jack.
a closer look, photo taken with my crappy mobilephone camera though
I'm not really sure as to what I can do from the back, there is a small hole where I can insert a thin tool but I can't see anything in there, and don't know how the locking mechanism works. I've tried poking around randomly but no luck.
I've also tried to poke something in the front hole where the push button used to sit, but no luck. The hole is so small that there is no chance of steering in any direction.
I've also tried to insert the little metal push lever/button but it is not possible without bending the small metal hook-thing that sticks out from it, possibly destroying it. So I did it anyway! But it seems this tiny bit is a crucial part of the unlocking device, so we have a catch 22. Cant stick it in without taking away the unlocking mechanism.
I like your idea, Laurence Payne, of soldering a female XLR on, as a last resort. Only problem is if I one day want to sell it, it would be harder to get a good price.
What to do now?