My first shot was wheat. Rye is a lot more expensive and bermuda ain't going to germinate this time of year. The downside of wheat is that it really should be covered and rye is broadcast on top of the ground. Forget about the perennial rye stuff. I have been told by seed people that it is rare that you will get it to come back with any consistency. If there is anyway you can scratch the dam to hold the seeds, it will help. You also might contact some seed seller like Justin Seed and Feed to get their ideas about heavy clay problems. I seem to remember that vetch does pretty well on clay but don't know about this time of year.