Bob, recall that project we did for ABC Corp in 2010 that I brought in under budget and well ahead of schedule that you said was A-one? Could you write a recommendation on my ability to produce high quality technical work in a very short period that really was on target? Please feel free to elaborate in your own words. And thanks so much for your help.
Bob will be able to work around what you suggested and add his own take on the situation. Then you are managing the output and also will get a far better recommendation.
You will be happier and can ask the next recommender to opine on a different aspect of your work and skill set. Makes sense, right?