Allow nested variables

I have a global variable:

job.config=my_job_config

And I have a plan variable:

maven.settings=${bamboo.job.config}/maven/myFile.xml

I've configured my plan to echo the maven.settings variable this way:

echo ${bamboo.maven.settings}

But when the plan is run I end up with:

Substituting variable: ${bamboo.maven.settings} with ${bamboo.job.config}/maven/myFile.xml

As can be seen, it did not resolve the nested variable to my_job_config.

I've realized that there's a paid third party plugin called Bamboo Nested Variables available in our Marketplace. However, if we suggest our customers to use this plugin and they have problems with it in the future, we probably won't be able to help them as much as we would like.