Practice without a uke
This sounds a little odd, but for strumming practice, you don’t need a uke in your hands at all!
As you probably know, all patterns (and non-patterns) are made up of up-strokes and down-strokes. Find the spot on your tummy where your uke would normally press, and just practice your ups and downs right there. You’ll be able to imagine the sound of the strum, without being distracted by the actual sound of the strum–in some ways that’s actually better!
Note: this really works.
Note: do not do this while wearing flannel. The static build-up can reach dangerous levels.