Shrink text size to fit text field

I have a PDF form created in Adobe LiveCycle Designer Enterprise Suite 4.  I need to make the text "shrink-to-fit" in a text field.  I've tried setting the font size to zero, setting the Field Format to Rich Text on the Object/Cell tab, and checking Expand to Fit on the layout tab.  When I Preview PDF, the result for that field is the text is very small, illegible.  I cannot find any documentation for ES4 that helps.  The form will be password protected, Fill in Form enabled in Acrobat.  Help!?!