I work in fundraising. So while I love this idea in theory, I'm concerned about the administrative costs involved. As much as we like to think there's a million or whatever Bills fans out there willing to support this (and I'd be one of them), you still need to get the word out. Direct mail, email, phone calls, whatever. That costs money. You need to provide paperwork and materials documenting individual gifts. More costs. You need someone to manage the fund itself and track the balance, likely provide quarterly/annual reports. If they get 501c3 status, then there's filing 1099s, all that stuff. More costs.
It's not just a matter of stuffing $170M in a giant piggy bank.