The machine that is used by most gyms to stop the dust from getting on the floor. Its called a hamstring curl machine, and it normally lives next to the quad extension machine, therein lays the answer to both parts of your question. Isolation.
Partial squats, considering it is the lower part that engages your glutes, I suggest that you only go two thirds of the way down. However this will prove tricky to know when to stop, and secondly will put stress on your knees.
I wouldn't recommend either, just stick to your real squats and tell people that J-Lo bums are fashionable.