I disagree in that there are plenty of ways to force Prescott out.
Who owns the media in Dallas?
If they wanted to the Cowboys could play hardball and leak stories to the media about Prescott capitulating in the games that matter, he's mentally weak, look at the state of him on the sidelines looking like he's about to breakdown as he's so weak mentally etc. They can drip feed stories and narratives that explode in the national media and let's have it right, he clearly struggles to cope with a lot of pressure.
Wasn't there an alleged DUI charge against him before he was drafted - this could suddenly appear in the media and then there's suddenly a narrative as to why he's so mentally weak and crumbles in the play offs.
Take away his locker and leave him out. Let him rot and test the market in a years time. The NFL doesn't sit and wait.
You politely inform Prescott all of the above will happen unless he agrees to a trade. If not then get toxic. He either does one or stays, if the latter then he will never play another down for the Cowboys, his reputation will be shredded and who knows where he ends up and how much money he will be offered in a year.