This problem has cropped up before, and as far as I know, the only way in is destructive - i.e. via drilling a hole in the tailgate (ideally, if the mechanic can work out where to drill, quite a small hole would enable you to trip the latch and get in - the hole could then be made quite inconspicuous with a pop rivet), and I know that some UK owners have had to have the rear shelf and chair area sawn into to get at it.
Does anyone on here know if another way has been found??
I've met people this has happened to, and they have been well annoyed at the consequences of a minor ding - or even the latch mechanism falling off. I dismantled my tailgate and installed an 'emergency release' line, a very fiddly job, but which would enable me to get in if need be and repair things without damage - but sorry, dirk, that is not much help to you now!!
I hope someone on here is able to come up with an alternative.
Lewis