I would think most retail level data feeds provide some type of aggregated trade reporting on their T&S. I use CQG with a block filter of 20, 50, or 80 depending on the time of day or volume level we happen to be experiencing. What I do, is watch the tape and if it is slow and see a 20 or 50 go through I honestly don't put much weight into it because it could just be an aggregate of retail orders going through at the same time. However, if the tape is moving very fast and I see 50's and 100's going across one after the other I can reasonably assume that a big player is moving some size, especially if it is moving the price.
in the old pit days you would give them a 30 tick range say for 500 to 1500 contracts it was always interesting to watch them get filled on a tick chart. you could actually see your trade getting filled.
clearly there are reactions just after commercial trades and i have been thinking about isolating and studying specifically those events.
Good luck figuring it out with all the nondirectional spreaders in the ES. Lots of size comes in that isn't a directional play, just a big player laying off risk or hedging against a basket of stocks or other indexes or (insert trading idea here).
if it were clear to see commercial blocks and you could isolate them you would probably have a edge. so i think it is worth while to pursue, problem is from what i am hearing "identifying"?