Cannot resolve active profile name at build time

I have a maven profile defined in my pom. It's not active by default, so I run -P <profilename>.
When the profile is running, I want to construct a path that includes the name of the profile. I've looked online and it appears that

http://stackoverflow.com/questions/2012198/maven-can-i-reference-profile-id-in-profile-definition

would have the answer. Alas, it doesn't work for me at build time. If I do a mvn help:evaluate -P <profilename> and use $

, I get the value I would expect. When I run in the build, though, it doesn't resolve and just uses the literal value in the path.