I came up with an interesting idea for a drill to work towards multiple opponents this weekend. We didn't get to play with this because we had other things to do, but you might try this and see what sort of mileage you get out of it. I know we'll be trying it soon.
Choose a kata that you are thoroughly familiar with, like releases or junana, and execute it with a second uke hanging onto one of your sleeves, or hanging onto your shoulders. You could do this with different levels of difficulty - for instance, it will be easier if the hanger-on will willingly trail along with Tori, mostly staying out of the way, so that Tori does not have to drag them around. Or it will be harder if the hanger-on were less mobile and compliant, forcing Tori to move them while interacting with the other uke too.
Either way, the hanger-on represents a challenge because no matter how compliant they are, they constrain tori's motion and take up space that tori could otherwise be using.
Try it - you might find it fun and interesting.