"you cannot attach the explanation to an efiled return "
I'm pretty sure that's just not correct. TurboTax will open a panel for the explanation.
TurboTax may handle this better this year.
Note: other tax software will handle this just fine.
" standalone form for a reason"
deficiencies in TurboTax is not one of the reasons.
"stupidity"
Stupidity is not "Reasonable Cause"
Yet, IRS always grants the waiver if you took timely action to resolve the issue.
