One of my favorite double front squat routines is double clean and front squat ladders, courtesy of Dan John:
Without putting the bells down:
1 DCL/1 DFSQ
2 DCL/2 DFSQ
3 DCL/3 DFSQ
etc...
You can progress this similarly to ETK. Start with a weight that is tough for 3 ladders of 3. Add ladders up to 5 ladders of 3. Take plenty of rest between ladders. Add a new top rung when you are able. You CAN do a heavy, light and medium day each week, although I don't think you really NEED to. It isn't a grind in the same way as press ladders. You have to stop, not because your legs couldn't do another squat, but because you're sucking wind and your abs are giving out.
When you get to 5 ladders of 5, you can keep adding rungs, although then you really should start waving the volume each week, or just start over with bigger bells.
Keep in mind that this is a lot of hinge reps with double bells, so you need to take that in consideration when programming other ballistic hinge drills. For instance, I would not do S&S type swings on the same day, and if you are also pressing, you might not want to clean before every rep.