A good place to do this is on the wood bridge where the Wookies spawn indefinitely on the Prologue when you control Vader. Just stand under the hut at end of bridge and let them keep coming to you...should have this one in no time.
EDIT: To do force grip hold right trigger and flick in the direction you would like to toss using left or right stick. As far as location you will see a TIE fighter crash into a bridge. Cross the next bridge and the Wookies will spawn infinitely.