I don't think there is any way to fix this, except to get a wood or real Fiberglass stock. The ABS stock flexes a lot in the front, which causes the barrel flexing.
I was thinking of making an aluminum inner frame for the front part of the stock so it won't flex, but I have no idea if there is room to fit something strong enough to help...
The TM SOCOM M14 doesn't seem to have this problem, I will have to check out my friends SOCOM again next time I see it. The stock feels a lot more solid, but it have the shorter barrel probably helps .