OK, this is totally geeky and I don't think I'd actually do this, but it would satisfy your intents:
Before your beverage in's coming from your keg, you could buy 2 of these (if you're trying to fill 3 cornies like me):
and thread one onto another to make a 3 port beverage manifold daisy chain (no one makes these, only y splitters like this one). I called them and they hooked one up to make sure the threads fit together. All you'd need is a washer in between.
and then have all your gas outs hooked up to a 3 way gas manifold that has your bleeder valve after that.
That way all 3 kegs fill to the same level since they are the same pressure.
That's pretty geeky, but it would work. Of course, you'd need the appropriate nipples and washers to hook up the hoses, etc..
EDIT- I re-read that you only want to fill 2 kegs, so one of these splitters would work and a 2 way gas manifold. What'ya think?
EDIT 2- Actually, now that I think about it, I don't know if I have the gas end of this worked out yet. What with the manifold and check valves and all...