You gave me some good ideas here, thanks.
I found som rather thick aluminium tape wich could do the trick as a guide. I will test it and hopefully it gets right, beacuse a 928 without rear end panel lines just does'nt look right.
Here are some pics of the current progress (after filling the panel lines):
Not looking to good at the moment...
BTW: I ordered a new kit today, just in case.. :-)