The SCLogin module is a stand-alone Joomla module. There's not currently a way to call the popup with a link without the SCLogin module being instantiated on the page.
If you want, you could include the SCLogin module on the page and then use CSS to 'hide' the contents of the module (the Login/Register buttons). From there, you'd have to look at the Javascript link that is included to call the popup and you could try adding that into a Joomla Menu item, but I'm not sure if Joomla allows custom links like that other than the standard a href links.
I hope that helps,
Alex
Login and My Account as on this page
