Nope. Only ordinary ambush groups without specified boss characters.
I did this in one of my arcs by picking a map which had a boss spawn relatively close to the final defend-glowy. The boss may be immobile, but he typically spawns within range and starts kicking your butt. (Which unfortunately was pretty brutal on soloers since he was an EB, but hey, it was my first arc. Didn't know any better.)
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Use the casino unique maps. The map is so small unless you're stealthed everything will attack you immediately 
Well, nerts. And between the placement AE bugs, trying to force the encounter doesn't work either. Thanks anyhow, though.
Quick question, as searching turned up nothing - I'm trying to find a way to make a named regular boss and his team-sized entourage make a beeline for you after clicking a glowy. Can it be done? I can make one or the other, but not both.