What are you trying to do with the clover? Are you going for green instead of brown, or are you trying to bring up some nitrogen? Would it matter if the grass were, say...nutgrass? Or does it have to be clover?
Before you plant your trees, if it is not too late, find out everything you can about a product called Actinovate. If you use that stuff to wash the roots as you plant the trees, they will surprise you with their vigor and health. The active ingredient in Actinovate is Streptomyces lydicus which kills the cottony root rot that seems to plague so many trees. Here is a website so you know what you're looking for.
http://www.actinoiron.com/list.html
This seems to be in the category of wonder drugs. The manufacturer recommends reusing the stuff, but from what I've heard, you only need the initial drench for trees. If you could soak the seeds that would be best.
Ask around in the trees forum to see if anyone is using it. Howard should know about it and how to use it.