Is there ANY simple way to add subtitles to an .mp4 for PS3?

I have heard of AVIAddXSubs which only works for AVI I guess, even though it says it supports MP4, which I tried to no avail. Is there any other easy program I can use to hardcode or softcode the subtitles to an mp4 file?

Not that I've found. I just turn the volume up when I'm viewing video files. Usually on Blu-Rays or netflix I'll put on subs though. I find it improves my comprehension of the diologue.