add blank lines in report builder

How do i print blank lines in my detail part of the report so that it always has a fixed amount of lines?

I am trying to create an invoice that takes a whole page. I want the detail part to always be, lets say 10 line, irrespective of the lines of data (there will be always less than 10).

I am thinking of using a rectangle shape, in the detail footer, with a conditional print expression. Probably there is need to create a user function that count how many lines are printed in the detail section. The result of the function would be subtracted from 10 and the conditional print expression would print the shape so many times.

Is this possible?

I am using LO Base 5 on ubuntu 15.10