Could bra-line back lift be extended to underneath breasts/around torso to remove large amount of loose skin in upper stomach?

Yes, this would be a reverse TT or abdominoplasty.  However this is not an optimal surgery. And it does not replace a vertical scar procedure in a person who needs it.Kenneth Hughes, MD, Board Certified Plastic SurgeonLos Angeles, CA

It would be helpful to see pictures.  I am not sure if your primary concern is the upper stomach or your bra line.  Typically for excessive skin on the abdomen after massive weight loss a "T" incision is made (a combination of a vertical and horizontal incision and the abdomen).  If this is not done, adequate skin removal may not occur.  At times, the top of the inverted "T" incision can have another horizontal incision right under the breast creating two horizontal incisions. One at the bikini and one right below the breast.  
I don't thing a torso incision as you have described will end up removing a large portion of skin on the upper abdomen AND result in good cosmetic outcome.  I hope this helps.  Feel free to post pictures if you would like further suggestions.
Dr. Dillon

Hi Set550, Thank you for your question regarding extending anteriorly a bra line back lift around the torso and underneath the breast to remove upper stomach skin.  Back lifts are commonly done to remove excess skin and fat of the upper back. Some people also call this a 360-circumferential upper body lift. The upper body lift gets rid of the skin and fat of the back, sides, and upper abdomen.  If you have excess back skin, the bra strap incision certainly can be extended underneath the breast and even meet in the front between the breasts. This procedure is called a circumferential upper body lift. On the front side, it is also called a reverse abdominoplasty or reverse tummy tuck. The 360-circumferential upper body lift is extremely effective to remove not only excess skin and fat of the upper abdomen, but also the lateral torso and upper and mid back.   If you have any more questions regarding the bra strap lift, back lift, back reduction, or reverse tummy tuck, please contact my office. Please seek an experience board-certified plastic surgeon who specializes in the bra lift, upper back lift, and the reverse tummy tuck.  Sincerely, Dr. Katzen.