How to generate the line to cut the paper?

Hello,

I'm looking for writing the line just at the limite of the paper size to tell to the printer where to cut the paper.
I use XEP to generate the PDF, my sheets are 13.5 x 21 and I write their on A4 paper sheet.
In xsl:fo, I tell that the sheets are 13.5 x 21cm, and I have margins inside, but after that I'm unable the use the leader to write the long dash, normally there is on with a circle just in the middle of the sheet, something like Xpress does.


Marc