Where will you be staying in the SLC area? Some hotels will hold luggage for guests before/after their stay. Maybe check with your property?

Or if that would be too far from SLC, check with a couple in town now, then book at one that does for that one night before your flight to DFW. Given the number of people who travel there with skis, I can't imagine that this is a unusual request.

Either that, or just make an appt at REI to get your skis waxed, then pick them up when you get back:
http://www.rei.com/stores/snowshop.html