Portal 2: Disable Cave Johnson voice in the Community Test Chambers Thread

Hello,

I need to disable the sound of Cave Johnson in the Community Test Chambers but I need to keep the other sounds on.

Could you please give me a way to do it?

I found the sounds in the .vpk file with GCFScape, but I can't erase them with it.
Then I tried to extract all the files, erase the sound files I don't want and recreate the .vpk with the Left 4 Dead 1 and 2 Authoring Tools (the only 2 I found that seemed to work). But after a while I keep getting this error saying 'Out of memory' Imageshack.com and I don't know where it could come from.
Any ideas?

Thank you