You mean you want the webauthentication screen to come up simply by connecting to the ssid? Not going to happen.
User must open Internet Browser and attempt to access an HTTP page before the redirect to the webauth page can be performed.
Now if your wireless supplicant had some kind of "launch program on connection" ability, then I supposed you could just launch a web browser. But you wouldn't be able to do that for Guest computers you don't control.
Bottom line, web auth redirect will only work when the user opens a web browser and attempts to access a webpage
