Thanks Radek, nice solution.
But i resolved by another way. In a custom webpart that i used in my print page, on the code behind i edited the PreRender event like this:
protected override void OnPreRender(EventArgs e)
{
this.Page.Header.InnerHtml = "..."
}
So, i override the header of the page, before the .net server render and show the page to the browser. =D