The imbedded form code that we provide from Formscentral doesn't have any notion of mobile or desktop. (It is the same HTML everywhere.) If you are wondering how to create an alternate layout with the HTML form embedded you would need to do that within your site code. You might check the Muse of Dreamweaver user forums for help.
Most mobile browsers now have the option of selecting "request desktop site" in the settings after they browse to a site on their device. You then refresh or re-navigate to the page. That would be handled on the user's end, not by your website or formscentral.