The easiest way to do this would be to have sticky bomb and replay side missions and encounters.
You can get at least 2-3 enemies grouped together on each and if you have a skill talent that recharges it faster you can get more.
Even easier if you are at least 2-3 levels above the enemies you can one hit them with the sticky bombs, so stay in the earlier parts of the story mission areas.
*EDIT* To be completely sure you will one hit your lower level enemies with sticky bomb, have your electronics upgraded substantially.