You can't, we were told by Intuit.  That's the limitation with all of Intuit's professional tax products.  In order to e-file a 1040X, the original return must have been previously e-filed with the particular Intuit tax product you are using.  It is evidently not an IRS MeF limitation - I am aware of at least one other competitor's professional tax software that allows the e-filing of 1040X even when the original return was not e-filed with it.