As a 'Referendum President', he promises to only shepherd one piece of legislation into law: The Citizen Equality Act of 2017.
He promises to resign once this is done, which causes his Vice President to take over as President. (I expect their ticket would also need a VP-in-waiting who the VP-turned-president would promise to make their new Vice President.)
He promises to DO NOTHING ELSE UNTIL THIS IS DONE. To me, that means he is promising to VETO everything else until his Citizen Equality Act is law. Congress and the Senate would have no choice but to follow the clear mandate given him by the electorate on this one, single issue. To do otherwise, they would be going against the will of the people and committing political suicide in 2 years... AND be forced to continue to deal with Lessig at every turn.
This would totally work, as long as Lessig stuck to his guns -- which knowing him and his passion for this issue, he would.