Instead of trying to figure out different convoluted ways for QBs to "give up" -- none of which will solve the problem of QBs "giving up" after a defender has committed to the tackle, thus putting defenders at risk of being hit with personal fouls/ejections/fines -- just go with the simplest, most elegant solution: treat QBs the same as any other ball-carrier beyond the line of scrimmage. The slide is stupid, and the fewer calls that are discretionary, the better. Refs could've fixed this by simply falgging QBs who take advantage of the slide by starting it late, but they're never gonna do that. Top QBs will always get the benefit of the doubt, so just remove all doubt.
You wanna run it? Are you sure you wanna run it?