There's gotta be a way to nudge those balls and freeze up the cue ball. I guess I'm coming back to your first assessment that you have to lengthen the game and probably play a couple lock up safeties. I'm not sure that it will take a critical error from your opponent, though. Depends on how badly you tie him/her up as to how critical the error has to be?
I've got it. I wish the diagram weren't a gif.
I'd bank the 4-ball into the 5/7 and leave the cueball snug on the rail. I may even have the cueball drift toward the lower right corner. I'd also hit it HARD. Perhaps a healthy rearranging will "turn the table" in my favor.