Installing Crown Molding - Metal Studs
Questions about rental/landlords aside, you could X nail with some construction adhesive and as long as your crown isn't huge (less than 5"), it should stay up fine. 

If I was doing this, I'd have temporary bracing (1x2s would be fine) while the glue sets, and add plenty of nails wherever the crown looks loose against the wall/ceiling.

One last tip you didn't ask for... when I do crown, I center it on the wall, shoot the middle to pin it in place, then do the corners with a bit of scrap (cut to the other side of the corner) to tweak the angle perfectly. If you have to twist a lot to make the corners right, then pin the corners and then pull the middle off and do over. If you just have to twist a tiny bit, then keep nailing. Twisting works much better on mdf than wood, obviously.