CSS: fly-in menu on a centred site

Designers that don't need to write code.... sigh.

Before I go back and tell him it's not possible, I thought I'd canvas the stackoverflow brain.

A centred website, with a slide-in menu. My understanding is that slide-in menus generally work by hiding the menu off the left side of the viewport. i.e. only valid on a left anchored site.

I have a site that does it by expanding the side menu (i.e. it can sit invisible with a width:0 but not sliding in.

via Chebli Mohamed