Thought of an interesting way to include Marion in Indy V without her tagging along, but possibly giving her a meaningful role (without other characters getting in the way).
So following the opening sequence, Indy is back home and teaching at Marshall (or whatever an associate dean does). At this point, Mutt is nowhere to been seen (either off at school, in the army, etc.). So like LC, the beginning is a little slow, w/ Indy and Marion being invited to a dinner of some sort hosted by friends/colleagues of the Jones'. At the party, we get our first taste of the macguffin as Indy talks w/ his colleague.
Late after the party ends, Marion and Indy are still talking, but at last decide to leave. As they are leaving, the film's villains (commies, other gov. agents, mercenaries) strike at the Jones' colleague friend (because of the macguffin). This leads to some sort of small action sequence (like the motorcycle chase in KOTCS, or the bar fight in ROTLA).
After this, Indy and Marion (and the colleague friend if he still be alive) begin attempting to figure out clues on the villain, how they're friend is related, and then the macguffin. After this, Indy (and possibly his colleague) head off on the adventure, leaving Marion behind (cause I mean, she dosn't really need to follow him).
So that was my bright idea. I'm writing this after a spur of the moment. I just thought it was good cause, hey, Marion is involved in an action scene, helps w/ riddles, and then probably appears at the end w/ no one else trying to take away her screen time.