I wouldn't. GR-2's are intended as stock replacement struts. You wouldn't put lowering springs on stock struts would you? Besides, if you actually care about the travel of the strut, you need to get a raised mount to offset the travel you just lost by lowering the car.
By the time you do it right, AGX's, springs, new raised mounts, bushings, etc. you are back into coilover price territory. Save the money up and do it right. A suspension is NOT one thing to go halfway on. For your safety and the rest of the people on the road.