Vw do a seatbelt plate fits behind the c pillar, you can get them on eBay,all you do is drill a hole where you want the belt holder , then drop a bit of rope through the hole down to were the belt fits at the bottom put rope through hole in seatbelt plate tie a knot pull it up and fix in place with a pop rivet
There are specific locations for the seats to be fitted. The VW kombi seat belts are located approx 300mm down the C pillar. He will need to add the correct vw plate. Part number 7HO 810 563. You will need 2.