This opens the dialog in the center of the screen.
RichPopup.PopupHints hints = new RichPopup.PopupHints(); //reference the instance of RichPopup you created through binding property <get method of your popup>.show(hints)
Presently ADF screens have been designed in BPM work space itself and data controls are given to the fields.Do you mean that you are using ADF Screens generated as default forms from a Human Task having Payloads as DataControls .. this should work fine as thats the standard way.
Its a registration page which has many fields.Will this work fine ??