download local file skin.xml from /usr/share/enigma2/HDSKINNAME

open in editor (notepad++ for windows or whatevere text editor for *nix)

searach for subtitledisplay

replace line with:

<screen name="SubtitleDisplay" position="275,150" size="720,576" zPosition="-1" flags="wfNoBorder" backgroundColor="transparent"/>

reboot or restart gui