I have exactly this setup for 2 customers.
(1 - A company with WiFi for visitors)
Just setup a generic username/password and edit hotspotlogin.??? so that the form has hidden fields for username/password which are pre-populated.
i.e. <input type="hidden" name="username" value="wifiuser"><input type="hidden" name="password" value="secretword">
The user will just then just see a button for 'login' - press to continue!
(2 - A hotel with Internet access in rooms / wifi in public areas)
Setup a generic username with a password of 'on', then edit hotspotlogin.??? as above so that the username field is pre-populated but for password:
<input type="checkbox" name="password">
The user will then see your splash/terms and conditions and can check the box to confirm their acceptance thereof.
Both of these methods work well and don't require any funny configuration other than editing the cgi login page (I use a PHP version but the idea is the same)