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Imagine this, you almost take a boost controller and use it to controll fuel cut. This may actually be one application where the mechanical boost controller idea would work well.

A very simple way would be to splice a bleeder valve into the line running to the solenoid and eventually the map sensor.

You would have to cut any wires! Only one place to connect. Basically idiot proof.

Seems possible, can anyone think of drawbacks?

We kind of discussed this in this other thread a while back:

http://bbs.legacycentral.org/viewtopic.php?t=1505

Morgie was using a check valve, which let the sensor read vacuum but not boost. I'd suggest something involving a relief valve that would allow the sensor to read boost but limit the maximum reading. There are a couple ways you could do that. The simplest would be a small chamber with a relief valve set to ~12psi venting to atmosphere, and then an outlet with a restrictor going to the sensor and an inlet coming from the manifold. Another would be a ball-and-spring setup that stays open until ~12psi and then closes.

A bleeder could work too... but then the ECU would always read the wrong pressure, not just when it "needs" to read the wrong pressure.

Either might be annoying to calibrate.

Instead of just putting a check valve in the MAP sensor wire, I put a T, and a skinny line going into the check valve, this way the MAP sees a little boost, I did notice a bit of an improvement over just the check valve also...