That would've been awesome. I think you're right - classic horse collar with the guy's hand inside Robert's pads between his shoulders.
But as boise said - nothing was going to get called on that play. Well - maybe if something really crazy happened, like the ASU defenders tackled all of the BYU receivers with the ball in the air. But it would've had to be crazy obvious. They rarely call something on a hail Mary to end the game, even when there is contact that isn't strictly conforming to the rules.