I suspect that your question may indicate a desire to wring more out of the text than is actually there. The Greek reads:
ETI LALOUNTOS TOU PETROU TA hRHMATA TAUTA EPEPESAN TO PNEUMA TO hAGION EPI PANTAS TOUS AKOUONTAS TON LOGON.
I believe that LALOUNTOS is a genitive absolute here, reinforced by the ETI, forcefully stating that it is while Peter is still in the midst of speaking "these words" that the spirit falls on those who are listening. But "these words" is no clearer in the Greek than it is in the English: most likely, it means "while Peter was still in the midst of making this speech", and does not refer to any particular set of words. If you ask me, the text does not clearly indicate that it was saying the last phrase in his speech that caused the Spirit to descend, and any theology which turned that into a magic formula for calling the Spirit down would go beyond what this scripture says.
Jonathan