Current status:

Custom filmstrip needles working
NeedleL and NeedleR animate correctly using setValue()
MatrixPeakMeter works
AudioAnalyser works
Both successfully monitor a ScriptFX processor when ProcessorId = "Script FX2"

What I'm trying to do now is obtain a real-time audio level value in script so I can drive the custom needles.

Things I've already tried:

Scriptnode core.peak
dynamics.envelope_follower
control.smoothed.parameter
Synth.getEffect("Script FX2")

Results:

MatrixPeakMeter and AudioAnalyser clearly receive valid audio/meter data from Script FX2.
Synth.getEffect("Script FX2") returns a valid processor object.
getNumAttributes() returns 0.
I have not found a way to access the meter values from script.

Question:

What is the recommended HISE 4.1 workflow for obtaining peak or RMS values from a ScriptFX processor and feeding them into a custom scripted UI meter?