use of the apostrophe

Paul's book - Paul is one person. The apostrophe goes before the s.

The boys' books - The boys are more than one person. The apostrophe goes after the s.

Pauls' is an unlikely situation. There are several people named Paul and you want to refer to something that belongs to these Pauls as a group. You're not really likely to see this.

I have a question about possessive use of apostrophes.

Sentence is as follows:

He lets go of her hand to shake Sean's. 

The hand is implied, not written, so do I use it with an apostrophe or without like "He lets go of her hand to shake Seans."