I don't know about 107's, but many German cars, like Mercedes 115 and 114's, of that era have an 'access plate' in the floor of the trunk that is just held in by a tar like substance. It can be pushed up into the trunk if you push hard enough and go slow while doing it.

Then you can remove a taillight and then you can reach the lock from the inside and, after unscrewing an access plate, reach the lock from the inside and remove it. You can then lift the trunk and repair the lock.

This takes about an hour, so no one will be able to break into your trunk while you are parked somewhere without it being seen.