Unfortunately, the option is system wide and other applications will suffer
Jono Bacon, Ubuntu community manager at Canonical Ltd, has shared some insight on a future option that will be implemented in Ubuntu 12.10 (Quantal Quetzal).The current state of affairs for Canonical's Ubuntu 12.10 soon-to-be-launched operating system is not good. The decision to implement an online search into the Home lens has proven to be more controversial than the introduction of Unity.
An option to stop the inclusion of online search results in Dash will be implemented, as we can spot from the screenshot provided. Unfortunately, the search will affect all the online searching, including, for example, Gwibber.
Any modifications done after feature freeze have to also gone through the translation department, hence the French menu tabs from the screenshot.
Jono Bacon also underlined the fact that all the Dash searches would be encrypted starting with Ubuntu 12.10 (Quantal Quetzal).