Remove the duct tape, clean the bar and the grip with min spirits to ensure that there's no oil or dirt residue on the bars, then reapply the grip. If the grip has embedded duct tape residue or dirt, you could try goo-gone to remove the adhesive, then min spirits to clean it up.
Never heard of the hairspray deal. May be a revelation and work great - but it won't if there's any oil, dirt, or adhesive residue left on the bar.
They use min spirits to apply golf grips. Get the grip and the bar wet, slide the grip on, position it, and let the min spirits dry. Works without adhesive.