Short answer: make your boss' life easy.
Try to provide as much help to your recommender, as it is possible without breaking ethical rules.
Combine all questions by subject. There are several common types of questions, and although they may be worded a bit differently from one school to another, the answer in many instances will be the same. Examples are: "History of interaction with an applicant", "Key strenghts", "Key weaknesses", "Reaction to feedback" etc. Explain that it's not writing 5 x 6 = 30 essays, it's much less.
Provide him with some exampls. THere are plenty of those available online, in admission guides, on forums etc.
Discussing "Why MBA" questions is also very helpful. You could explain your motivation and application strategy. For example, "I am going for an MBA to get further career progress in our industry - I think, that I need to develop X, Y and Z skills to make the next step, and I already have an experience of demonstrating skills A, B and C on projects Alpha, Beta and Gamma. etc". The result is that you boss actually knows the logic and knows what's relevant and what's not. Discussing all this stuff you both will mention lots of good examples worth including into his recommendations and your essays.