I would assume that you were referring to QWP for SP2007 as in both SP2003 and SP2007, there is option "Edit in datasheet" whereas in SP2010, you would click on "List" ribbon tab and access through Datasheet View. For SP2003 and SP2007, adding this feature is possible but we no longer provide new feature in QWP for SP2007. However you can easily work around by the following steps:
1. Add a custom action as a toolbar button, name it "Edit in datasheet"
2. Define this action to be associated with a "GoToUrl" action
3. Copy the URL that OOTB ListView use when you click on the OOTB "Edit in datasheet" link and use that URL in your action class, you may specify additional parameter if OOTB one requires
4. Now save the settings and view the web part, click on newly added toolbar button to go to the OOTB editing datasheet view
For SP2010, I would assume you can work around it as well but since this is invoked from Ribbon UI, more research needs to be done in order to figure out what actual URL link is used or Javascript is called for the datasheet view – you could possibly use IE developer tool or Firebug for Firefox to intercept and debug the call to find out.