I was surprised to learn that the parts house actually had reducing washers for 2-1/2" pipe. I was also pleased when I was able to trim the washers with my aviation snips. Here's the result:
Now, this is not the first time I've had to deal with this issue. I was hoping for a better solution - or, perhaps, some trick to prevent it from happening in the first place.
The longer I'm in the trade, the less I like those pre-punched KO's!