Paul wrote:

Can I put two large
screws with spring toggles, or similar, into the wall and just suspend
the mirror off those?

Spring toggles need the screws to be permanently pulled up tight. You'll
need to have the screws projecting from the wall to hang the loops on so
the toggles won't do unless you use them to attach some sort of hook to the
wall. Hollow wall anchors like
http://www.screwfix.com/app/sfd/cat/pro.jsp?id=12229&ts=89915 should do
the trick. Screw it up tight on its own first to expand it then back the
screw out enough to hang the mirror on it.

--
Mike Clarke