Believe you'll need to edit CBs router.php file and create custom rewriting for the URLs extra parameters as it has no handling for those parameters.
lastly, do you have any plans to add a sign up module so we could place a module somewhere other than just the subscription's pages?
Probably not as CBs registration is dynamic and site by site. It can be large. It can be small. Often it's always large. So a module display would be awful.