Let me see if I can clarify a bit. Suppose I've got some Ethylene in ME fluid storage (from Extra Cells). What I'd like to be able to do is use small amounts of it (e.g. 144 L) in processing patterns that involve converting it to one type of plastic (polyethylene, PVC, PTFE, polystyrene, etc.) depending on what I need at the time. As far as I can tell, AE2 and extra cells do not offer me a way to do that. I think it's possible to set up an autocrafting pattern using cells of fluid, but I'd have to fill the cells manually in the fluid terminal, which somewhat defeats the purpose of having an autocrafting pattern, and I'd have to make larger batches of whichever type of plastic. I don't follow how a Thermal Dynamic servo would help with that.
You can do this exactly with Extracells.
You code a machine/processing pattern with the exact amount of fluid in a container. Openblock tanks can do, Large Steel/TungstenSteel GT cells can do, and GT++ offers you 144L exact cells.
Then place your pattern into a fluid export bus to your GT Machine.
It will export the exact amount of fluid and items to craft using fluid on-demand.