Shoutbox

Making an invisible button is simple, just give it a custom look instead of a custom gradient.

<CustomLook>

you give it a hot, normal and pushed thing as with the customgradientand if you leave the custom look tag empty, it'll be invisible, if you want text where the button is, just put a StaticControl inside the custom look tags.  Basically with custom look, you can make a button look like any other control or element.  You could scrap the image element and put it inside the custom look for the button instead.