Well, one of the main reasons to have templates is to create a separation of concerns. Mashing everything together seems counter to that (if I'm understanding you correctly). Other than Eliya's suggestion I can only think of something like Text::Template (There's also Template::Toolkit but that's definitely going to be more than one file) having the ability to mix and embed in that way but you will still have two files. Sorry I can't be more help. Maybe with a little more clarity a few other monks can assist you.
"...the adversities born of well-placed thoughts should be considered mercies rather than misfortunes." — Don Quixote