We do this a lot, it's a great drill.
Two ways to mix it up:
1) Vary the target distances. For example: Target 1 at 2m, Target 2 at 5m, Target 3 at 3m, Target 4 at 5m. Really works your eyes to acquire the front sight against the slightly different backgrounds.
2) Work in an early-reload, or a feeding failure. For example, have your buddy load your first magazine with a unknown number of rounds and/or a dummy round (no powder) somewhere in the stack of either your first or second mag. Work past the problem and finish the drill.
3) If you carry a backup gun, work the "New York Reload" into the programme as well.