I know that this has already been addressed as a straight up trade.

Here's how a trade with DALLAS might make it less of a drain on the running attack.

TRADE

RB/FB Lex Hilliard 5-11 240 and DE Tony McDaniel 6-7 305 to DALLAS for

RB Marion Barber 6-0 225 and DE Marcus Spears 6-4 315.

Why Dallas would do this:

Gain Salary Cap space (to sign Miles Austin long term) and gain a RB/FB type runner (similar to Barber but younger) to join their three-headed rotation of Felix Jones and Tashard Choice (they could also afford to draft a RB in the later rounds for depth and use Hilliard as a FB).

Pick up a developing athletic DE.

Why Miami would do this:

Allows Miami to trade for Vincent Jackson without completely depleting their running game.

Ricky and Marion Barber could carry the load by sharing it.

Parcells likes Barber and trusts him.

Miami has plenty of DE types who don't have enough bulk to play NT. Here I would expect Miami to try to convert Marcus Spears to a NT. At worst, they have a starting caliber DE. I think that Marcus Spears has potential to be a satisfactory (Jason Ferguson-like) Nose Tackle. He buys time for Miami to draft and develop a rookie NT. Right now there is nobody at the nose tackle spot.