you can't use 'hidden' b'cos that is relying on a viewer's client (and i mean client not browser here) to understand css. that's not the same people who want a text only version (unless they're a bit odd and backward in their ways, i imagine nielson surfs with images turned off as standard).
imo, if you're pressing a button that says 'text only' it should be just that, text only. as the stick says, it should be accessible anyway if built properly.