Where are you finding that the election must be made at the time of efiling?  The 4547 must be used to "elect" an account, at least for now, but it doesn't have to be filed with the first return, whether electronic or paper, on which the child is claimed.  From the instructions:  "Even if your child is not eligible for a pilot program contribution, the election to open an initial Trump account must still be made on Form 4547. For more information, including whether you can make this election online beginning in the middle of 2026, go to trumpaccounts.gov."