The plugin should pick up the github.account settings from settings.xml (or maybe some environment if there is a convention). When resolving a repository, it will check if there is an appropriate fork of the project on the given github account. If such a fork exists it will be cloned as origin and the authorative repository will be added as for instance "apache" (based on hostname of origin, probably). In such a case, the project can always be pushed to origin, since that represents the github fork.
Interesting thoughts in this netbeans feature request: