At its roots, a hack squat is just a quad dominant squat. This gives you a lot of options if your thinking about the purpose of the exercise which is to load the quads in a stretched position.
Consider a quad dominant free weight squat variation. Maybe a quad dominant split squat or Bulgarian split squat variation. These are both easy to set up. The only downfall is you lose the stability the hack offers. But, you gain the freedom of movement for your joints right to left which is a plus.
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