I came up with a work around for this too.
On the join page I got rid of any and all buttons that link to the join form that lets you create an account with just your name and email address.
Then I used the "add a section" to create a "form" that had all my personalized membership form questions on it.
When you hit submit on the form there is an option in editing to have a confirmation page shown OR a redirect page that automatically takes you to a landing page.
So I created a payment page with my membership options that is unlisted and can only be accessed using the auto-redirect from the form submission. Then they select their membership option, pay, make an account, etc. but I have already gotten the membership form filled out from them and can go from there.
Hope this helps!