Granted it's not ideal per-se, but I'm running the stock USDM map, no exhaust avcs connected, and a VF40 on my EJ20X and it runs absolutely perfect! I only tuned out the DTC for TGVs and that was it. I don't know if I manually tuned it that it'd get any better.
I originally bought a JDM ECU also but no one in Orlando wanted to program the immobilizer so I just worked with what I had on the US one.
I haven't opened them up, but I bet you could flash the JDM map onto the US ECU. The pins are probably connected internally just not read for the exhaust AVCS. May be worth a shot?