Non-standard engine sounds

I have an unpowered E unit being used as a cab on a push-pull passenger train. I’d like the decoder to produce a diesel engine sound of an HEP generator, at fairly low volume and fixed RPM. I figured I could use a sound decoder, put a dummy load across the motor terminals, and program the engine parameters in the CVs. But I looked at a list of NMRA CVs, and didn’t see suitable entries - only a file selection. Would the volume and rpm be included in the sound file?

Similarly, how do you set up sound for an F40PH in HEP mode? Special decoder? Special sound file?
"Similarly, how do you set up sound for an F40PH in HEP mode?"

An F40 running with HEP on (at least on Amtrak) would be in notch 8.
Whether the engine is standing or moving. Throttle position 8, all the time. Around 893rpm.

There was also a "standby" mode, which could only be used when the engine was standing. It would switch the main alternator over to providing the HEP, and the diesel engine would run at throttle position 5.