How do I depend on a port regardless of its flavor?

I'm working on a port that depends on a port which is flavored.  If I do 
this:

RUN_DEPENDS= foo:devel/foo

That works because the lack of version spec means the LHS is a file to 
look for, and /usr/local/bin/foo will be installed regardless of flavor.

But I need to also specify a version spec.  However, if I do this:

RUN_DEPENDS= foo>=1.2:devel/foo

That only works if the default flavor is installed.  If one of the 
non-default flavors is installed, the Ports System doesn't find it and 
tries to build the port.  Similarly, pkg thinks I need to install the 
default flavor.

The flavors aren't part of a framework like Python, so I don't have a 
set of variables I can use to construct a universal pkg name.

How do I add a version-limited dependency on a flavored port?