Good point, ULCard17. I think the one ACC team that still is working to sign a contract for a 4th non-conference game is Boston College. Everybody else already has four.
You have to get the non-conference games set first, because if you do it the other way around, it becomes very difficult to find someone in another conference with an open date to match yours.
One possibility is for BC to play at UCF ... but I haven't heard of this advancing beyond the rumor stage.