If you manage for large bluegill, you will have a glut of 10-14 inch bass which will have no interest in eating your ducks. I've fished ponds like this my entire life and never, ever witnessed a largemouth eat a duck. If you don't harvest any bass they will become lean and mean, which will keep your remaining bluegill fat 'n happy. I'm conservatively estimating that I've spent 10,000 hours on the water. The biggest terrestrial item I've ever seen a bass take was a mouse. If your bass are generally small I just don't foresee a problem here.
Now if you do choose to go with no largemouth, then you'd have management options like I've got. I feed the bluegill and put heavy harvest pressure on females. It works out just fine, but I also have some hybrid striped bass which probably help a little, and some yellow perch which are probably eating little bluegill in my pond as we speak. It's do-able.
