How to show custom tags (e.g. replaygain for audio files)?

[anijatsu]

I'm not sure if this isn't a feature request.
I'd like to add in a few tags related to replaygain to the context menu displayed with mediainfoex. I can see that the application makes use of FFMpeg, and I know it can already read the tags I'm interested in:

ffmpeg -y -loglevel error -i file.flac -f ffmetadata flac.txt
(...)
**REPLAYGAIN_ALBUM_PEAK**=0.97711897
**REPLAYGAIN_REFERENCE_LOUDNESS**=89.0 dB
**REPLAYGAIN_TRACK_GAIN**=-5.75 dB
**REPLAYGAIN_TRACK_PEAK**=0.97711897
**REPLAYGAIN_ALBUM_GAIN**=-6.70 dB

How can I add them to be displayed with mediainfoex? The default options don't mention them.