The sneaky elastic fix has saved many a too-big cuff and stretched-out neckline. It's a specialty of the Whatever Works School of Fine Knitting.
Use round elastic thread and a yarn needle (white for light colors, black for dark colors, transparent if you can get it). Weave several rows of the elastic through the ribbing inside the cuffs, starting and ending at the seam. (For a man's sweater I'd use 4 or 5 rows.) Pull up each row of elastic as tightly as you want it and fasten in the seam.
The ribbing hides the elastic and the cuffs fit snugly. It also works for ribbing that starts out the right size and stretches over time.