If your offensive units are facing some really tough well dug in defenders, bring a few workers up behind your invading army a square or two behing or to the side of your armies. The AI just looooves workers and will bring troops outside of their defenses just to try and nab a worker. Of course you can then easily pick off their lone bandit however is most advantageous of you to do so.
Even if they capture your worker you can capture it right back, no loss. Heh.