Quoted:
9mm buffer?
I can't believe no one else suggested this seeing how it's the cheapest, easiest and IMO best solution. You can get a Colt 9mm buffer from PK Firearms for $25 and not only will it add a little more weight to the rear but will also lower felt recoil, increase lock time which leads to more positive extraction and helps lower bolt bounce. All my AR's with carbine receiver extensions have 9mm buffers installed and have so for years now without the slightest negative issue.
Going to a fixed stock with an rifle buffer is also a good solution but a fixed stock may not be your cup of tea and unless you have one laying around, that will cost you more money then a 9mm buffer. A heavier carbine stock like the SOPMOD, ACS or UBR will help too.
From there all you can do it lighten the front end. Looks like you are using a DD Omega 12.0 which is already pretty light but if you replaced the Omega with an 11" Troy TRX Extreme BattleRail you could loose around 6oz which is pretty significant. Just those 2 changes would make your gun lighter and make a huge difference in the way you gun handles and the CG.
What is the profile of your barrel? If its an Bull or HBAR then having it re-profiled will also make a big difference.