I know this is old and may not apply anymore but I send my child's in by mail. I type in on Adobe my child's name "By my name, parent for minor child." Then sign the exact same way under signature part.
This way I can talk to the IRS, because the 3rd Party Designee is only good for 1 year. It sucks that we can't e-file because there is nowhere to sign/input that.
