Ah, but that requires Javascript. Any email client that supports Javascript (already a fairly tall order, because of security concerns) ought to have it locked down, no?
I'm asking for a bit of a miracle, I know.
This option works in the Activate Direct (my web based mass email system) preview areas. Any php or javascript methods work in neither the email reader nor the activate direct preview window. However, this non-Javascript method doesn't seem to work in the Gmail web interface, although I've yet to try Outlook. If it doesn't work in Gmail web interface (on IE6, that is), it's still fairly worthless to me.