The form is rendered inside a page controlled by something else higher up.  So we can't recreate a <head> section here.  Though you can just include .js files at any point in the page, you don't have to include in them in the <head>, that's just good form to do so.  But it will work from anywhere.  

In our case, the best place to put these inclusions is probably the drawJavascript function in modules/formulize/include/formdisplay.php.