I like the HEREDOC syntax, e.g. for edge cases of generated HTML that are not worth putting into a template.
The only thing that annoys me about it, though, is that
That's a problem I often have too : the code is not well indented when I use heredoc, and I really like heredoc :-(
A "bigger" problem is when you select a whole block of code, press "tab" (or any equivalent in your IDE) to indent it more because you added a condition arround it or anything... And it breaks the heredoc strings : you have to go un-indent them by hand :-(
Unfortunatly, I've never seen any tool like the one you're describing...
A solution, I suppose, would be to put the heredoc string in another file, and include it -- the include like could be indented normally ; but it would also mean one more file to load, which would make the code less clear.