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The only difference is the O2 wire and ECU. The CA model uses a 4-wire narrow band O2 sensor while the Federal model uses a 5-wire wide-band (which is $$$). I believe the Federal ECU is the P07 model. Unlike most other Honda ECU's, it cannot be modded.
On GS, one member made the sensor/ECU swap on his VX and still easily passed his CA smog inspection. For those who care, NOx can be partially dealt with through a NOx adsorber as used on the Insight. The Insight entered lean-burn much less often (and less aggressively) and purged the adsorber through enrichment, but its basic operation would transfer over to a VX.
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If you're sure the motor will work, do the Federal ECU swap. The 4-wire sensor is a dead giveaway that the CA model doesn't support lean burn.
I'd imagine this absorber "purging" process cancels any benefit from burning lean.
John, how are you certain you're in open loop, is the O2 unplugged? I tried doing this on my Cavalier, but the variation in AFR was too wild to run reliably for any length of time. I would advise against slowing down your pump. If it produces less pressure than the regulator needs to open, the fuel supply line will slow to a crawl and the return line will stop. Depending on the design of your pump, it may be cooled by the fuel that runs past it, which will not be much if you go below regulator pressure. Try finding an adjustable fuel pressure regulator instead.
Be careful if you do this, because you will have leaned out your WOT mixture as well. If you need a sudden burst of acceleration, you could cause severe detonation. My car stays in closed loop at around 16.5:1, but if I stomp it, open loop is still around 12.5:1, so I can still get full power out of my engine safely.