Also can't open the boot, but for different reasons. During a recent autocross event the battery mount loosened and the battery was flying around in the trunk. During my run it actually caused the boot to open. In the paddock I was able to look closer and see that the battery has about 2-feet of cable slack and will slide far enough towards the middle of the car to snag on the interior glow-in-the-dark boot release. It looked like that's exactly what happened: battery came loose slid into boot release, popped boot. I slid the battery back to the side of the trunk and shut the boot. It was never to open again! It seems that there is damage to the lock/latch mechanism.
Symptoms: the key won't turn the lock. There is something preventing it from unlocking the latch. No amount of effort from the key will result in an unlock.
I have reached into the boot by carefully lifting the back edge of the boot lid and placing a coat hanger around the interior release. No joy, it seems to be already pulled all the way out. No doubt damaged by the sliding battery.
I have also been able to reach through the engine cover louver with a 10mm 1/4 driver ratchet and remove the nut holding the striker pin to its mounting bracket. It's loose and wiggling around in the bracket but will not push backward and out of the bracket. I don't see a way to get a small hammer in there to try and tap it loose.
I've pulled the bottom engine cover and just had a look up. Nope, there's nothing to be done from the bottom side that I can see.