Muxing external subtitles into MKV on the fly

I have a Panasonic Viera TX-P42G30E and with PanasonicViera2011DTS profile in use, everything works perfectly.
Well, almost perfectly, there is one little thing that makes streaming MKVs little bit less than 100% convenient for my use cases.

I watch lots of MKVs and since English is not my first language, most of the time I choose to whatch videos with subtitles.
The TV supports MKV container and can also display internal subtitles without any problem if they are embedded in the MKV file.

It is however not able to display external subtitles for MKV files. I don't really know if it's because the TV does not support this (my guess) or Mezzmo is not even trying to stream external subtitles with MKVs for this TV, but I was not able to make it to work simple by trying different settings (subtitles tab of device properties). I even tried to modify the device profile myself to enable remuxing to MKV (since currently only mpeg/mpeg2video/ac3 and mpegts/h264/ac3 are possible), just for the sake of trying, but, as expected because of my limited understanding of profiles and integration with ffmpeg, it did not work.

So, if I want to watch MKV with subtitles, I always have to start mkvmerge from MKVToolNix tools, and mux the subtitles into MKV file. (with one TV specific setting - disable compression for subtitle stream, otherwise my TV will have problems playing the file).

What I want to ask is:
Is there a way to make Mezzmo to do some magic so that I can watch original media content (not transcoded ! just a stream copy) from one MKV file with subtitles stored in another external file ?
Something like simply re-muxing the MKV while adding new subtitle stream(s).

It's not something I consider to be a unforgivable deficiency of Mezzmo, it can do lots of cool things already. Just little thing I miss.

Thanks.

Please email us at support [at] conceiva [dot] com and we'll provide a device profile to try.