BluRay: splitting subtitle track to forced and non-forced

[me7]

I want to transcode the BLuRay of the movie "Borat" with x264 and mux it to mkv.
The movie contains one english subtitle track that contains both forced subtitles (for on-screen text) and subtitles for dialogue. Suprip can extract the forced part only, but is there a tool that can do non-forced only?

[0xdeadbeef]

Why would you want to not display the on-screen text that is there even if subtitles are deactivated?
The extraction of only non-forced subs kinda contradicts the idea of forced subtitles.

[me7]

Because the on-screen text does not consist of normal subtitles. The video stream is language independent and contains grey boxes which are meant to contain text from forced subtitles. This text needs to be displayed at a certain font, in a certain size on a certain part of the picture. Since muxing untouched BluRay subtitle streams into mkv is possible but playback is problematic, I thought that the easiest way would be to hardcode the forced on-screen text subs into my encode and add the non-forced subs as .srt to the container. The non-forced subs are just dialogue, the position and size does no matter.
Do you understand the need?