I didn't think they could be efiled.  From an IRS email back in early July:

Taxpayers who used the “Non-Filers: Enter Payment Info Here” tool to register for an Economic Impact Payment and need to file a 2019 tax return must file a paper 2019 Form 1040 or 1040-SR tax return by mail with “Amended EIP Return” written at the top and pay tax owed by July 15.

The Economic Impact Payment’s Non-Filers tool was not intended to be used by taxpayers who also needed to file a tax return with the IRS for tax year 2019. If you used the tool to register for a payment, you cannot file your tax return electronically. You must complete and print a paper 2019 Form 1040 or 1040-SR tax return, write “Amended EIP Return” at the top, and mail it to the IRS by July 15. If you owe tax, you should pay it in full by the July 15 due date. Interest will be charged after July 15 on any amounts that are not paid by July 15. 

These same instructions apply if you registered for your Economic Impact Payment using the IRS Non-Filers: Enter Payment Info Here tool, tax software, or a paper tax return indicating $0 or $1 of adjusted gross income. If you have a copy of the document that registered you for the Economic Impact Payment, you can include it when you file Form 1040 or 1040-SR.

Tax Professionals please note that returns labeled “Amended EIP Return” will be processed as superseding returns if submitted before July 15 or, with a valid extension, before Oct. 15.

Rick