Well that's a damn good question which I don't have an answer for.
When filling out a NYSP "P-12" the caliber, and barrel length are part of the questions... I suppose "frame only" could be supplanted, it's done on 4473's.
I suppose
you could let your sister buy the frame, and have her sell it to you thru a NYS dealer, then recieve it as a "used" frame since it was previously sold/papered thru an other individual.
Just tell the dealer it's "as new in the box".
Used handguns do not require a ballistic sample.
Keep in mind that this is a grey area but play by the rules and no one could can say squat. YMMV