Disable keyboard entry during Edit Mode

[RJ]

Hi, I would like to disable keyboard entry when during edit mode. I have setup custom tool that user can use to make changes but not to enter any text directly to my Editor. Its like all keys on the keyboard is not allowed. I already made use of preview mode with my custom tool so that user cannot enter in any characters, but with my custom tool it can only do highlight or change color of the text but not able to change the word. For I think pastehtml not working with preview mode. So in order  to make pastehtml work it should be done during edit mode but then again I don't want user to enter in any text thats why I wanted to disable any character entry.

I think this can be done via javascript, but I don't know the code on disabling all keys..

Thanks in advance,

RJ