Do you have a removable carry handle?
If so you could just chop the carry handle with a dremel and keep the rear sight portion and create this yourself:
http://www.bravocompanyusa.com/LMT-T...ight%20l8a.htm
Personally, I like:
http://www.laruetactical.com/larue-t...buis-qd-lt-103
If you don't have a removable carry handle and you don't want to use a cantilever mount, your best bet would be getting a drop in free float rail.
This is what I use on my rifles, and it was quick/easy to install:
https://www.primaryarms.com/Daniel_D...p/dd-10001.htm
If you don't use a Free Float rail that is tied into the upper somehow, you won't be able to hold zero (the handguards wiggle) and I honestly don't know if it will work like this. I ASSuME it will based on seeing this done with rifles with monolithic railed uppers.
But, there is some flex with the DD Omega rails that I have when you push hard on them and I believe it might cause a zero shift.
Removeable handle is best, cantilever/ARMS SWAN sleeve is 2nd best, FF Rails would be my last choice.
Hope this helps.