Is this like, "I have a friend with a problem . . ."
Bill Hartman may pop in and blast my input/theories to smithereens. But . . .
1. Lighten the load and have them only do the movement the proper way. They have to do it right first before they can do it more/heavier. Form first!
2. In lieu of the above (or in addition to it), do unilateral work: split squats, lunges, bulgarians, step ups. I would think use the same load and do the same reps on both legs (do only as many as the weaker side can handle).
3. Do some assessment of postural and related imbalances. Get the JP summit DVD from last year with Bill as the presenter. Great presentation. Alternatively, get Bill's golf flexibility DVD and/or Gray Cook's book or book and DVD.