heredoc question

How can I include "place holders" for variables in a heredoc such that after the heredoc is declared, I can assign the variables? I have a config file with a heredoc string declared. I'd like to keep the include config.inc at the top of my page. Down in the page, when I call the heredoc variable, I'd like to replace the "place holders" with a values assigned in the page, below the include statement. I know I can break up the heredoc into several segments and put the variables between them; but, I rather not. Seems like there should be an obvious way to do this. Thanks...