Sub-domain plugin form on primary domain

Any chance you can give me some insight to making the zip code proximity search form located here: call the database from a sub-domain ??? My scenario... Store Locator Plus plugin is installed to the sub-domain " which houses the db tables for the locations and store pages created by the plugin and the proximity search form I need lives on the home page " (if you visit the home page you can see the non-functional form in its dummy dev state) How can I make this work?
I need the form on the primary domain homepage to function using the form from this sub-domain page ( retrieve the data and publish to another page (not yet created) or just any page but the home page.