Without using GET parameters, you only have a couple different possibilities.

Big Kludge (not recommended) - Use LWP to submit the query and get the HTML, then display to the client. The query doesn't come from the browser so hokey stuff is going to happen.

Cookies - Store the information in cookies and then redirect.

Sessions - Give each user a unique session ID every time they login and pass that with GET. Store the information that needs to be submitted in a flat file or database.

The reason for all this is because POST works by sending the input through STDIN. That means you can't cleanly recreate it on the server side because the client must be involved to properly use POST.