I think
http://oddworldlibrary.net/media/oswsubliminal.wav is the full reverse message. I can't check on this computer as it doesn't have any sound, but I'm confident it's what you're after.
I'll just add that credit goes to
Boneho Chane for first noticing the reverse message, to
Mr Pottymouth for first supplying the recording in reverse, and to
Cort for this file.