Brett,
I remember in an old Super Chevy(?) an article on modifying a Holley regulator so it was referenced to engine vacuum.
It was fitted with a hose fitting on the diaphram side and a hose run to the intake.
High vacuum gave low fuel pressure, low vacuum gave full pressure.
Might be able to do what you want too.
Disclaimer: I have a suspicion I'm forgetting some important detail.
Q: Do you have to use a marine carb on your boat?
Any Coast Guard regs for turbocharged engines?
