[Groff] setting page offset on page 1 via pseudo page break?

[Joerg van den Hoff]

I thought I had this solved but cannot find it again (neither
in my stuff nor in the docs):

`.po' requests (and PO register in `ms' which I actually use)
do take effect only on the next page, i.e. after page break.

question: how to enforce some page offset on the very first
page without either editing the default value in the groff 
macros (very ugly) or some kludge such as starting the document
with

.pn 0
.bp
.\"here goes the actual document starting with page no. 1

I seem to recall that somehow one can enforce a pseudo page
break so that e.g. the page offset is honored without actually
emitting a page. or is this wrong?

joerg