What I did on my M4, and what I suggest to you, is to attach a rail sleeve. Something similar to the A.R.M.S. SWAN sleeve that will attach to the front rail (around the barrel) AND the upper reciever will work great. I forgot the brand I have, but it's an airsoft replica, and only cost about 75 shipped. It creates a continuous, uninterrupted rail across the entire length, from charging handle to front sight post, and makes it incredibly solid.
Mine is installed on a metal body, but you might run into trouble if you install it on the plastic reciever of the stock TM SR16, since the upper rail (which is metal) is not permanently fixed to the upper reciever. I suppose if you use threadlock on those hex head screws it will be ok, but it won't be rock solid unless you use a metal reciever.