1. Build an Unity app with App Store validation on.
2. in info.plist update values for
-Bundle version
-Bundle versions string, short
-Bundle identifier
3. Codesign app with:

codesign -f --deep -s "3rd Party Mac Developer Application: " testApp.app

When launching the app you need to use a sandbox account (see comment for details)

In order to upload to the Appstore with Application Loader,

1.you need to add:

- 'LSApplicationCategoryType'
- 'com.apple.security.app-sandbox' entitlement
- ICNS icon package

to the .plist file

( I'd recommend using http://u3d.as/4TN from the asset store, because it does this automatically. )

2. Build the installer:
productbuild --component testApp.app /Applications --sign "3rd Party Mac Developer Installer: " your.pkg

3. Upload the package with ‘Application Loader’, it should appear in itunesConnect after a while.