how is it possible to use a variable in features.xml file?

I define it as stated in  http://fusesource.com/docs/esb/4.2/deploy_osgi/DeployFeatures-Create.html and how should I use it?

file:$/foo-bar/1.04.00.01-SNAPSHOT.jar</bundle> .... but it doesnt work, smx doesn't resolve $

how shall I do it?

thx