Space Shuttle External Tank Launchers

I could've sworn I saw Henry Spencer state recently (or I stumbled
over it in a newsgroup search recently) that the Space Shuttle's
external tank by itself had the mass fractions to be an SSTO if you
bolted 6 SSMEs onto its rear. Naturally, I can't find that statement
now that I'm looking for it.

Whether or not Mr. Spencer even said that, the idea is interesting to
me, and generated a couple of questions:

1) Could the ET be converted to an (expendable) SSTO, or be used as
the basis for an SSTO in such a fashion?
2) What would be the ballpark payload to LEO?

Mike Miller, Materials Engineer