Good news everyone.

Just found this http://www.med.unc.edu/www/newsarchive/2011/may/unc-study-pelvic-widening-continues-throughout-a-person2019s-lifetime
Seems like the pelvis always continues to grow and is never really totally fused.

"The pelvic width of the oldest patients in the study was, on average, nearly an inch larger than the youngest patients. This one-inch increase in pelvic diameter, by itself, could lead to an approximately three-inch increase in waist size from age 20 to age 79."

Would be actually interesting to know if one would be able to assist the growth, for example through adding some growth hormones to the usual hrt regimen and doing hip opening exercises on a daily basis.