XSL-FO: limiting lines per page

Hello,

    I'm developing a j2ee application  where I use the latest version of FOP
(trunk) because I need the latests developed features.

    My application returns mtiff images but with text inside, no pictures.
Each
tiff of the mtiff is a page of a document i'm returning in a web service.

    As the document I return has legal implications it has to respect a
determinate format. The problem I have is that even pages need to have exactly
24
lines and odd pages exactly 20. There is no problem with the diferentiation
between even and odd pages, but I don't know a way to control the lines per
page.
Is there some?

   In fact, the document don't use tables. It have a text like format, with
blocks, paragraphs and lines. Block titles count one line, and there aren't
white
lines at all.

   Any help will be welcomed, thanks in advance!