18.5 BMI - should I gain weight for a facial fat transfer? I am getting a lower bleph and facial fat transfer in 3 months.

Right now, there is not enough fat on my abdomen to graft, but there is plenty on my thighs. I have narrow hips, so I'd rather keep fat in that area to feminize me. Should I try to put on 5lbs so the fat an come from my abdomen? So that though time weight gain is distributed in a more hourglass form? Or is the graft so small that it will make no difference. I have a BMI of 18.5, so gaining 5 lbs will not be unhealthy. Thank you!