Thanks for posting your idea, AC! We know that having a more options for Sign Up form is very good feature for your site. We’re looking into this and we’ll get in touch with you once we start working on it. Thanks again for your suggestion!
For the mean time, as a Pro user, you can get the HTML code from Sumome on the form you created with them. You can paste this code on your site by heading to your site editor >> click on Add New Section button >> select Apps & HTML section >> select HTML >> paste your code on the field provided. Don't forget to hit SAVE when you're done!