Subs are hard to read

I bought a LG BP325 Blu-ray player. Its ok, but the external subtitles (for mkv, mp4, avi etc.) are really hard to read (when there is something very light in the picture, because they are rather small, white and they have no border). There is no way how to change the color of the subtitles or add a border to them in the menu of the player. So I was wondering, is there a way who to make the subtitles more visible? Some kind of hack? Thanks for any help!