Here is my solution (if anyone is interested) of mounting 3 point seatbelts, -the roller is inside of the rear armrest, and one of the two clips that held the original factory seatbelts at the headliner is now tucking the seatbelt against the rear armrest (at bottom) when not in use.

-Note that here in Denmark it's mandatory that you have a 'real' 3 point seatbelt. -plus alot more ssafer too!!