The major issue for the Cavs in acquiring the 13th pick from DAL is the fact that their most likely use would be to package that pick to get a top 10 selection. Due to the possibility that DAL will lose its 1st rounder in 2014 they cannot trade the pick before the draft, but instead must make a selection and then trade the player not the pick. There is however a simple solution to this problem which would allow the Cavs to land the 13th pick ahead of the draft.
Solution: return the Mavs pick from OKC. The Mavs pick is top 20 protected for 5 seasons and then unprotected so it is not wildly valuable. The Cavs could offer a very similarly valued pick by giving up their own top 20 protected pick for 5 seasons and then unprotected to OKC, return the DAL pick to DAL + two second rounders for the #13. Dal loses the cap hold and gets a 1st rounder + the second rounders back it desires.
Obviously there is no incentive for OKC here but it shouldn't take much for them to benefit- cash and a future second rounder might do it or perhaps taking some of the protection off the pick- ie making it top 18 protected for 5 seasons.
For the Cavs they pick up the #13 pick for a heavily protected #1 and 2 second rounders while keeping the #19 pick this year to package with #13 to move up.