wp_create_user with URL string

So what im trying to do is the following…

the client wants wordpress installed externally of there server but secured so no one else can access it unless through there site (long story).

so they want an iframe to display the page when a user is logged into there own website.

once the user is logged in,they click on “blog” this link should pass over url variables into my wp blog and create a new user (so the user does not have to login twice basically).

i was looking here, http://codex.wordpress.org/Function_Reference/wp_create_user

i was wondering if its possible to add new users with a url string?

for example:
link: http://www.website.com?fname=John&sname=doe&pass=pword&email=my@email.com

then some how i would need to parse this and insert it into the wordpress add user function.

wp: <?php wp_create_user( $username, $password, $email ); ?>

any ideas? possible?