This is an issue of signature techonology, not of Constitutionality. If you want to amend the Constitution to require hand-signature by ball-point pen, have at it ... but the current Constitution does not address the issue.
Autopens did not exist in the 18th century - when the Founders said he had to sign it, they meant he had to personally sign it ...
They also said that you just could not deviate from the Constitution - unless by Amendment.
Ball point pens also did not exist in the 18th century. Every bill since the advent of ball point pens must be unconstitutional.
Signing by an implement other than quill & ink is not a deviation from the Constitution. No amendment is required because there is no langauge in the Constitution that needs to be changed to allow signature by ball-point pen or autopen.
SnakeDoc