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If you don't know how to flash a rom or root, just head over to XDA as there are pretty simple guides, or you can use the root toolkit for the nexus 5.
I haven't tried it yet, but apparently if you have root, you can install this app https://play.google.com/store/apps/details?id=com.riteshsahu.DataController2, and it'll work if you convert it to a system app (can use titanium backup to do that), haven't tried it yet myself though.