Originally Shadows of Lylat needed them before we came around.
Karajorma also invented a King of the Hill mode that he discussed in the FRED
section ages ago... both gave rise to how we'll do it.
Essentially, it's all in FRED'ing.
Set your powerup model in place.
Set it up so the model will disappear when approached within a certain distance.
On that event, produce the effect on the ship that was within the trigger zone.
Have a respawn time set for the powerup, run a check before the powerup is to
respawn that the space isn't occupied already (camper), if not - spawn model.
That's the basic idea, although I can't quote sexps.
Basically the player ship never touches the model, it's just the source of a event trigger.