How do I depend on a flavoured PHP port? The Handbook is wrong??

I'm trying to add a dependency on a flavoured PHP application, but the 
Porter's Handbook (section 7.3.1) instructions don't work.  It says to 
just add "@${PHP_FLAVOR}" but that's an empty variable.

I can't add php:flavors to the USES line because that then requires this 
port be flavoured as if it were itself a PHP application (it's not, it's 
just a metaport).

Adding "php" to USES works, but adds an unnecessary lang/php?? dependency.

What I need is the PHP counterpart to python:env, but I can't seem to 
find it?