Okay, scratch that last comment - I got it added just fine without an error.
New problem... With the plugin now referenced through the link you provided, I pushed the project to the Testing Server in the Intel XDK Test tab. I then loaded the project via the Intel XDK mobile app and the same problem continues... The phone still goes into screenlock/sleep mode.
As I'm aware, the Test tab (testing server) in Intel XDK doesn't support 3rd party plugins, you have to build the app and then test .apk file.