Membership registration using modal option to a pricing chart?

Hi, I'm working on a site using the Membership plugin. I've created a pricing chart with a button at the bottom of each column ("Join now"). Each of these buttons links to the appropriate registration page for each of my subscription levels. However, I'd prefer if rather than linking to a separate page, the registration modal opens instead. How do I configure so that the links I've plugged into the pricing chart (which currently link to new pages) will instead show the modal?