Abdomen Filler - is it possible to create a 6 pack?

A better option for you may be abdominal etching This is a form of liposuction that helps to define and contour a given area, in your case the abdomen. Visit with a board certified plastic surgeon near you to learn more.

Normally, I would advise against trying to create 6 pack abs with fillers but if you already have abs and want to accentuate them like in your case, it is possible to do that. Sculptra, Radiesse, or Bellafill would be the best products to use. Bellafill is the most permanent. You should find someone who knows what they are doing or else you will waste a lot of money and risk having it look ridiculous.

In short- YES, it is possible to use filler to address the asymmetry and irregularity you are describing in your abs.
That said, the most common dermal filler types for this purpose are composed of Hyaluronic Acid- these generally degrade about 12 months after injection, and are usually sold by the vial. So what you're describing could quickly become an expensive and recurring annual cost to maintain the results you're seeking.
An alternative treatment to address what you want, is minimal abdominal liposuction/etching and fat grafting to help sculpt the more "normal" appearing 6 pack that you desire. Not only will the fat survive much longer (minimizing the need for annual repeat treatments), but the minimal liposuction used to obtain the fat can also help further define your abdomen and flanks and make the results look really impressive. This treatment can be done as a same day ambulatory procedure in the operating room, or sometimes even in the office under local.
My recommendation is the abdominal/flank liposuction with fat grafting to sculpt the more normal appearing abs. Best of luck!
-Dr. Donald Groves