I think you’re right, I believe it has a solenoid that provides vacuum to the EGR, but there are no electrical connectors going straight to the EGR. Should I try unplugging that?
You could try, see what happens.
This still seems related to the ECU entering closed-loop mode (although I've assumed this, based on your description of the situation), and I'm mulling it over.
See, when the ECU enables the EGR it also reduces the fuel flow (injector on-time); simultaneously, if the EGR doesn't flow enough exhaust gas, there will be excess (and unconsumed) oxygen remaining after combustion and the O2 sensor will detect the lean condition (Code 44). Too, the engine performance will suffer at these times. This is why I'm focused on EGR.
What I would try is to disable the ECU from enabling EGR. The only way I can think to do this, with your ECU and EGR set-up, is to prevent the ECU from entering closed-loop mode.
There are a few ways of doing this, and probably the "best" way is to disconnect the O2 sensor.
In the later models, like my 1998, the ECU can tell if it's connected to the EGR and, if it believes it's disconnected, it will disable EGR.
IF YOU disconnect your EGR electrical connector, and drive the vehicle for long enough, the ECU will probably figure-out that the EGR's not working, set a code / SES and disable EGR operation. This would be ideal, in the short term, for you, if it worked; but I don't know how long you would need to drive it for this to happen. Once it happens thou, it would be obvious by the SES and / or set code.