We can play a game real quick. As of right now the Cowboys are 12 million dollars over the cap for next year. Assuming they cut Cooper that will put them 4 million under the cap (giving them enough to sign draft picks). Now if you were to trade Dak, which would presumably happen before June 1, you would have an extra 23.5 million in dead money to deal with (basically giving a grand total of 58 million in dead money cap hit next season or almost 30% of the cap) which would put you about 20 million over the cap. There is no way to get around that number with creative cap numbers. To get that 20 million back you would have to cut DLaw, Tyron, Jarwin, Greg, and Brown (in addition to Cooper) which when taking in all 5 is an additional 40 million in dead money bringing the grand total to 98 million in dead money. Now if you were determined to go this route you would of course designate DLaw the post june-1 cut and make next years dead money hit 88 million (or over 40% of the cap).
You do ALL of that you could afford to trade Dak but there is one more problem... Rodgers wont play for free and you have 4 million in cap space. I am not even sure there are enough cuts to even pull off some creative signing bonus, but you would REALLY not want to see what that looks like