Custom Flite Voice (with .flitevox file)?

I’ve got a custom Flite voice generated (output as a .flitevox file) that I’d like to use with Rhasspy. I put the file in my profile directory, and tried setting the voice in the Flite TTS section to ${RHASSPY_PROFILE_DIR}/custom.flitevox but Rhasspy seems to be falling back to the default Flite voice instead.

Not sure if I’m doing something wrong, or if this isn’t supported with the way Flite is being used in Rhasspy.