This is now possibly the easiest way to do regional prompting in comfy on 1.5 models. Requires a secondary application which uses comfy as a backend and it's not 100% on point (which is perfect because instead of trying to fill in a box with an object, it tries to place it around that area in a way that it makes sense overall) but I have high hopes it will improve.
Haven't tried it with multiple girls at the same time yet.
https://github.com/mut-ex/gligen-gui