Not sure if have resolved this already. If you have not, please follow the steps provided by Sandeep earlier to retain the build output files, that is the first step.
Secondly, open the Eclipse installation from the Android SDK installation and Import … > Existing Projects Into Workspace …> (Select the path of your project)/Builds/<Version_Number>/<Handset_Name>/temp/java_edit
This will open a project on your Eclipse installation with the project name as NativeUIDemoGalaxyS2EN (if you opened the NativeUIDemo Project with a Samsung Galaxy S2, ENglish build).
Right-click on the project and now Android Tools should be visible, and then click on “Export Signed Application Package…” and follow the Wizard. If you dont have a signing key, the tool will provide you with the option of generating one.