Hanging temporary doors and then replacing
If you order cheap slab doors and the fancy doors from the same supplier, then swapping the old for the new should be extremely easy and not prohibitively expensive. 

Though it might seem like you're burning money, ordering both cheap and fancy as pre-hung units should mean that it's just a couple of hinge pins, a doorknob move, and you'll be swapped. The door casing isn't a major part of the price of a prehung door.

** caveat on the "should" is that hinge spacing might vary and it then becomes a bit more carpentry to fix it... but if you inform your supplier in advance of the plan, you've got better odds of success.