I wonder if there's an altitude you could do a "landing" at that would be thin enough atmosphere and weak enough gravity to get close to Martian conditions.
NASA does indeed use high-altitudes on earth to test Mars aerobraking, atmospheric entry, and supersonic parachute deployment[0]. For the actual terminal descent and landing speeds are low enough the atmosphere is not significant, you can just test that at sea level.
Gravity will still be too high, gravity at the ISS is 0.89 times gravity on the ground and you obviously need to be lower than that. But it's definitely the closest we can get to a large scale martian atmosphere.
