URL Encode to send as form POSTed Items

Hi All, I would like to know if it's possible to use php to encode form variables as if they had come from a post form instead of a get form. I imagine I need to place them into a header but cannot find much to read that gives any information on this. I need to create form variables and than use header location to direct the user to another page that will process the form. I'm posting to another site which is why i have to use form variables. I would like to avoid using JavaScript as this takes longer, will not work on all machines. Thanks Zac