S.L.
I'm not sure why you need to wean him just because you are going back to work. My son nursed when he woke up and before he went to bed and it never interfered with my work. If he will drink water during the day and eats a balanced diet I don't know if you really need to force him to take breast milk or formula from a cup. You can also talk to your pediatrician about other options. At 11 months he will probably be fine without bm or formula and you can switch to cow's milk, soy milk or another milk alternative.