Override jspm config file path (and name) using "config"

[pkapare]

I am trying to override default path and name of JSPM config file (config.js) using "config" parameter as mentioned in documentation however its not working and gulp still searching it root directory. I am trying to use same gulp file to build two different sub applications having different JSPM configuration. Is there any way I can override JSPM config file path and name? I know we can override path in package.json however I am using same package.json for two applications hence I can not use package.json to override path.
Thanks & Regards
Pankaj