The meter output is designed to replicate what you are listening to so an external meter can visualize what you are hearing. A fold-down on the meter output would “break” this concept.
However, there is a work-around.
1. Define a 7.1.4 meter output and send it to for example the coax MADI output (or any other available output) and loop it back into the coax MADI input.
2. Create a second monitor group in your monitor profile.
3. In this monitor group, you define a 7.1.4 source assigned to the coax MADI input.
4. In the same monitor group, define a stereo output which you connect to your meter.
5. Add a 7.1.4 to stereo fold-down to this group.
Once that is defined, simply enable/select the fold-down in this monitor group and you have what you asked for.