What is it that you want on the XLT that isn't on the XLS? Make up a list of the differences and try and price the parts out...unless you want to make the jump from the I4 to the V6 (I'm not sure what yours is, sorry).
And I suspect the dealer will be happy to do this considering its a used car trade in, and I'm sure their offer will be not what you expect, remember the "off the lot depreciation" will kill you. Plus you'll be stuck with all the new car fees, freight, admin, tax, PDI, etc. all over again. They will not make it easy, or inexpensive for you. :doh:
You'll be spending a couple thousand bucks more, for a slightly better model with a few more features? Thats why I said price them out first thing, you may find spending $1000 on purchasing the XLT tidbits is way less expensive that trying to swap your car out for another.
But if this is a I4 or V6 problem, well...all I can say there is remember the Escape is not a fast car, no matter what engine you have. The difference isn't worth the added expense the second time around if you ask me.