Exercises for side butt area?

[RubyBlue]

I don't really know how to describe this; but I have sort of a flat butt in the main bit, but the side bits sag a bit more than I would like.

So I think what I'm asking is: is there anything specifically that I can do to firm the side parts up? I'm not overweight.

I know you can't spot-reduce; it's almost like I need a redistribution of material from the side to plump up the glutes proper, if that makes sense!

It's sort of saddlebags but more to the side of the glutes. It's probably gravity more than anything.

The obvious answer is 'squats' but I can't do these or lunges due to my knees. At the moment I'm doing Physique 57 and yoga, as well as Leslie.

So any specific exercise suggestions would be great, please: pretzel, maybe?

It's not a big deal at all in the grand scheme of things but I'm curious if anyone has any suggestions, or has solved a similar issue.

TIA.