I'm not sure if this is already a feature, I've tried but it would be nice to enable or disable subtitles from the ps3. If its already a feature I'm sorry. If its not here is how I think it can be done.
There can be a folder on the computer that is shared, in the folder it has a small video named 'enable subs.avi' and another small video named 'disable subs.avi'. Both videos are about 100k, no big deal in file size. When you play the 'enable subs.avi' video on the ps3 and ps3 media server streams it, it can trigger something in the program to enable sub titles and vice versa.