Many surgeons will recommend you do these procedures separately for this reason. If you choose to do both together, you will need to understand that you are at a higher risk of loss of the buttock fat grafts.
I would recommend a cigar shaped pillow to be used on your gluteal crease. This will help prevent direct pressure on the fat grafted areas.
I wish you a safe and healthy recovery.
Web reference: http://www.drpaulgill.com