I don't have KDE installed, however, I'm wondering if maybe they do it like some other apps do... vncviewer, for example uses the "-" key (zoom out) for the middle mouse button and the "+" key (zoom in) for the right mouse button. In vncviewer, I hold down the + key and then touch the screen with the stylus to get a right click.

Probably not, judging by some of the comments above.