That would be my favourite quick-fix method. Alternatively, raise the brood box by inserting strips of 'something' underneath it - say, 3/16 inch plywood. (which you should be able to cut with a utility knife)put it in front of the entrance. The bees usually will not push it out of the way.
I bought some cheep hives at a big box store on sale once LOL - same problem - Just push them up close and put some Garlia tape on each end mSand paper works wonders on entrance reducers.