I took a quick look at the VB scripts that handle nudge/tilt, and it looks to me like you should be able to get your scenario working simply by using my copy of the nudge plug-in - that is, go to your VB scripts folder, and rename NudgePlugIn_mjrAccelAndTilt.vbs to NudgePlugIn.vbs.
That script is really set up to work with a physical tilt bob, but if I'm reading things correctly, it should also work with VP's built-in simulated tilt bob.
The key is that the script does the main thing I mentioned that you'd have to do - it translates a key press on VP's "Center Nudge" key, usually mapped to the Space Bar key, to a simulated pulse input on VPinMame's tilt switch.
The last I looked, when VP's simulated tilt bob is enabled (via the Tilt Sensitivity setting in the VP keyboard options dialog), it sends a Center Nudge key to the script when the simulated tilt bob detects too strong of an accelerometer input.
So the plug-in script is doing just what you want - it translates the simulated tilt condition to a VPM tilt switch pulse, letting the ROM know that the tilt bob triggered.
There are a lot of moving parts here, and it's all kind of jury-rigged, so I could easily be missing something.
If you give it a try, let me know if you have any luck - I'd like to add a mention of this to the build guide if it actually works.
One quick test you could perform to make sure the script is working would be to simply press the Space Bar key while playing.
That should immediately trigger a tilt warning message in the ROM, as though the physical tilt bob fired, without generating any simulated physics nudging. If that much is working, and your accelerometer is generating physics effects in the game, that leaves only the VP simulated tilt bob (the Tilt Sensitivity thing) as the troubleshooting focus if it's not working overall.