This won’t work with Dak because the dead cap Dallas will take has already been paid to him. I’ll give you an example of what you’re thinking of:
Cleveland owed Baker Mayfield 18m in fully guaranteed salary this season. They wanted to trade him, but no one would take that deal. So Cleveland agreed to pay 3/4 of his salary to get him off the books. When Dallas trades Dak, all of his salary goes to the other team. The only absorbing of salary that can happen is if Dallas agreed to pay some of it for the new team, which is the opposite of what you want.
But the big cap numbers and dead money Dallas takes on in a trade is because of guarantees they’ve already paid Dak that are spread to future years. It’s not money you can get back unless Dak agrees to write Dallas a check for 30m$, which will never happen. Restructure (guaranteeing he’s a cowboys for more years and requiring an extension next year), extend now, or trade & accept the massive cap hit. Basically the 3 options.