Looking for ideas for a "let someone else drive you" objective

I've been making a mission where at the start you're arrested. You have to get in the back seat of one of two police cars, and they drive you somewhere. The front seats of both cars are occupied with the driver and a guard. I set up most of the mission and put the cars there with a "go to vehicle" objective, kind of a placeholder because I knew the logic would have to be set up later. Now it's later, and I am kind of stuck. The Problem: the mission can have anywhere from 1-4 players. There are two cars with four available seats between them. I need to have the drivers wait for all players to enter either vehicle, then take off (both have "follow path" tasks) convoy-style. Struggling to wrap my head around a way to do this well, though. Go To Vehicle (my placeholder objective), if set on both cars, requires you to get in both, even if there are only 1-2 of us playing and only need one car. Also, that objective will consider each vehicle "gone to" if just 1 player enters, unless I set the car to require more players or the entire team, but there may not be enough players to satisfy; if you played it solo it would be impossible to advance. Some thoughts I'm toying with: - I could replace the go-to objective with Holding on a short timer. Basically the players have x seconds to get in the cars, which then drive off with or without you on the start of the next objective, and if you aren't in the cars, a mission flag zone spawns in the area they vacated and causes you to fail. Clumsy but effective, I imagine. - I could maybe do something weird with mission flags. For instance, a small flag zone box that encompasses just the two cars, set to "outside area" (so the real zone is everywhere else BUT the box), with "clear flag on exit" checked. I haven't been able to test this yet but the idea is that if any player is still NOT in a car, the mission flag is set; as soon as all players get in, it clears, because they've all left the zone. Then all I have to figure out is how to make clearing a flag finish the objective or make the actors start driving, somehow! I assume the latter is possible if I think about it enough, just not sure if the zone logic will actually work the way I think it will (that is, any player being still in the zone will stop the flag from clearing). Looking for any thoughts or other ideas. Unfortunately not one police vehicle seems to have more than 4 seats unless you hang off the car, which would be really silly for this. And letting players drive themselves is, as they say, not very immersive.