number of rows on a Detail Area

I am developing a custom version of AP20. The Detail area (with GL account etc) has 5 lines. I want to show only line #1 to the users. I was hoping to change the "rows" property of the Detail object to 1. When I click on the Object - properties, it is greyed out. I tried changing the "rows" property on the source. It seems to get reset to 5. I tried setting it in the script
 
Form_oninit()

vFld = lawform.getElement("DT0",0)
vFld.setAttribute("rows",1)

does not seem to work. What options do I have ?

Thanks.

Ragu