We are going for a rustic/outdoorsy/casualness type of wedding. We have moss green table runners with daisy trim, for example.
However, our venue is not really in the zone for that. It's not a typical ballroom, but it's really not very rustic-y at all. Huge floor to ceiling windows along two walls overlooking a garden (might be covered in snow), a unique ceiling that I really can't hang anything from, and some greenish patterned carpeting.

How can I decorate (cheaply) to make it more outdoorsy? I can't hang anything from the ceiling or the walls. Also, we only have two hours day-of to do all the decorating. So for during those two hours we have to set up the runners, the centerpieces, placecard table, cake table, and the foyer area. So it's gotta be something quick to put in/set up.
Any ideas are most appreciated!