How can I dynmaically use page-number?

I am trying to place a unique barcode on every single page that is rendered.
Right now my code is hard-coded to the barcode generator:

<fo:external-graphic height="1.2in" width=".35in"
src="http://localhost:7001/barcode?code=0401&amp;degree=270&amp;caption=t"/>

Which is telling the barcode server to return a barcode for page 1 of 4.

Ideally, I would like to do something like this:



<fo:external-graphic height="1.2in" width=".35in"
src="http://localhost:7001/barcode?code=04<fo:page-number/>&amp;degree=270&a
mp;caption=t"/>

Which, of course is not valid XML. Anyone have insight on how I might go
about accomplishing this?

Thanks

-andrew