Well there is Sopot....so players can play week after Wimby, then Fed Cup, then Sopot, then Helsinki. Three tournament is enough on the clay considering Vienna was played earlier this year.
Also, if I remember correctly, the tournament in Denmark was never on clay in the summer. It was always taking place indoors in the fall, and as far as I know it still is, but I haven't checked the calendar in a while.
Venus Williams-Ana Ivanovic-Serena Williams-Vika Azarenka-Caroline Wozniacki