Create choice control with choices populated by previous selections in the form

Greetings,

I would like to create a drop down field where the choices are populate from previously filled in fields filled in on the form.  ie;

The following fields are filled out on the form first

item 1

item 2

item 3

later in the form the user is presented to select from a choice of the previous fields selected

Item choice:

{item 1}

{item 2}

{item 3}

any ideas ?