If the skin has loosened in the donor site enough to lift it more, a second uplift can be very helpful. The result would typically fill in a dented area but wouldn't add true roundness.
Fat grafting has been tried with disappointing results. One way to add true roundness back to the gluteal area although requires a lot of hard work is to work out the gluteal muscles enough to thicken them. Any improvement in the gluteal thickness would be noticeable in the shape of the buttock but again requires a lot of gym time!
I am very happy to hear you are doing well and my pleasure to be of help to you,