Universal recommendation

You certainly want your references to answer the questions on each school's application form. Assuming your recommenders are open to your guidance, one way to ease the burden is to do some analysis for them and group similar question types across recommendation forms. Group questions together in a grid to show them where they can use the same response or a slightly modified response across applications. For example, almost all recommendation letters will ask how long they've know you and in what setting. Many schools will ask them to compare you to your peer group, and so on...

This approach has two benefits. First, it will give your references some comfort that they will be able to leverage much of their work across multiple applications, and second, your grid will provide them with a handy guide to follow when doing so.

Finally, the more you can do to support your references in general the better the outcome will be for you. Consider giving them some brief suggestions on major messages to cover and a project or two drawn from your work together that they might touch upon in their letter to feature key themes and messages.