simple answer would be to give campos and usa a 4 race amnesty, then let stefan run the first 4 races. after 4 races if as seems likely one or both of the two missing teams don't show up stefan can carry on. if both turn up then the team(s) in last place in the constructors championship and the 2 latecomers have to pre qualify with the fastest 2 teams on combined driver's best laps being in the race. this should give stefan the advantage to ensure they stay racing and it should weed out which ever team is way off the pace. after a further 4 events the prequalifying would be for the 4 teams that were lowest in the championship.
as an added bonus it would give us something exciting to watch on friday and in fact it could be turned into a 10 lap sprint qualification with once again the agregate team results deciding who gets into saturdays qualifying, the grid for this decided by fastest times in an early 30 mins practice.
one further bonus is that it would also give the teams that were at the bottom of the championship some extra track time and some publicity