How to read the value of a form field in OAF page and pass it to Destination URI of a custom button.

I need to add a custom button to the Customer Address OAF page and call a custom form (fmb) and pass a parameter value to it.

I have managed to add the button to the Address OAF page by completing the following steps

Chose Personalize "Account Site Address"
Added a Button on the Header Address level (Populated ID, Additional Text and Prompt properties).
Also set Destination URI=form:SYSADMIN:SYSTEM_ADMINISTRATOR:STANDARD:FND_FNDMNMNU.
The button is now showing in the address page, and when I click on it it opens the seeded Menu form.
I now have to create the custom form and set Destination URI to the Custom Form and pass a value to this custom form read from the OAF page, so that it launches the custom form rather than the menu form.