Is it possible to have a Custom Sign-up Form?

I have installed the 'Supporter' plugin and it all looks great in the dashboard. Did I read somewhere that it was possible to have a custom sign-up form rather than wp-signup.php?

For example, like you have here where the user clicks the 'sign-up' link and instantly gets choices of 1 month, 3 months and 12 months.

Maybe I was dreaming but I'd like to do that if possible.

Thanks.

Martin