The Irish. You can't deny who they are and what they bring to the table. If you're the BIG12 you have to try and lure them in.
How? You offer them the big dogs seat. You pay them (purely guessing on what I've read) 70 million per year, offer Clemson (or another at large), Washington, and Oregon 50-60 million, and the remaining teams 40-50 million. Of course those numbers are purely speculative and would probably have to be higher to get the job done but you get the gist.
Why? Because quite frankly Notre Dame has earned it. Give them their dues, suck up your pride, let them be the flagship of the conference. Offer Clemson, Washington, and Oregon tier 2 money not because they are any better then the rest of the conference but simply because they would strengthen it significantly moreso than the other teams I've read as targets.
Why allow the B1G and SEC to just run away from everyone else. If the BIG12 could land those four it would put them solidly on par with the other two conferences and provide Notre Dame a means not to be forced into the B1G (which I don't think they really want) and force the playoff committee to recognize the top 1 or 2 performing BIG12 teams as legitimate contenders.
Of course this may not be possible for Clemson if they ACC truly has a lock on their teams for 10-15 more years but they are not the kingpin here. It's the Irish. We might not like them but it's worth a shot to go after them.