There's a constant flow air valve available from Badger for the 100GB which is the "bakery" edition. If you go to the Badger website and download their price list it's listed with the other parts for the 100G. As the 100LG is the same AB with a larger cup, the valve would fit.
I've never heard of a modeler requiring one, and can't imagine using one. If you're concerned about controlling the paint flow, then I suggest the 200-20 with the PPS Paint Metering System, that allows you to dial in the needle position fixing the line thickness. Otherwise the air flow is controlled by the on/off operation of the trigger.
I would also be concerned that the compressor could handle the constant running. Many people buy compressors that are oil-less and they heat up very quickly. Badger sells a Bakery compressor that maxes out at 10psi and runs between 3-5psi. Rather low for spraying model paints, IMHO.