[Blarg]

Inform the players that there will be a "reciprocity rule." The Bad Guys will respond in kind to escalating violence.

If the PCs start making head or groin shots, so will the Goon Squad.
If the PCs bring Vibro-Plasma Axes to a fist fight, then the Goon Squad will bring Vibro-Plasma-Nullifying Mega-Swords next time.
If the PCs start sniping, so will the Goon Squad.
If the problem becomes too bad, then the Goon Squad will suspend the "line up and attack one at a time" rule.

If the PCs come in shooting, perhaps the Goon Squad will simply retreat and call the Planetary Patrol about the blaster-waving crazies in the Town Square.

Make it advantageous for the PCs to allow a monologue. For example, The Evil Emperor does not know that the PCs sabotaged his Voice Activated Mega Force Field so that it is now running on Emergency Power. They now have a reason to keep him talking until the power runs out.