Get your taxes done using TurboTax

I have the same question but no one seems to be able to answer it.  What is the actual process of e-filing a return as a POA for a person who is incapacitated etc.  The answers that I have seen say to mail in form 2848 and 8453 but do not provide an answer on how one electronically signs a return via turbotax on behalf of the actual taxpayer.