I'm afraid there's not much you can do once the painting is actually finished to speed up the oils drying, other than applying gentle heat, which you're already doing. You needed to have used some rapid-drying medium in the painting.
All I can suggest is to put the paintings under a lamp (not closer than about 10 inches, you don't want to cook the paint) and think about constructing transport boxes that'll allow for the paint still being wet (use hard foam or the equivalent to keep the packaging away from the painting). Or try the clips you get for transporting wet canvas when plein-air painting (though these may damage the front edges of the painting).
