Pro sites wp-signup.php redirects to upgrade page

Hi guys!

I've got a problem with my Pro-Sites multisite. I'd like my customers to be able to sign-up without seeing the pricing table, by visiting wp-singup.php and signing up there. Unfortunately this page seems to redirect to the pro sites signup page every time.
To resolve this issue I tried adding the anti-slog plugin and redirecting the sign-up page. With anti-slog redirecting the correct page does show up, but the signup path doesn't seem to create a successful signup either, with the template selection directing users back to the start of the signup process again.
Please help!