I tried to do this a while ago while playing with the RadScheduler. I don't think there is a way to adjust the control from the client-side. I think you can adjust the width from the server-side PreRender event for the RadScheduler. The control will need to re-render after the window is resized, so that seems like a logical place to change the width. Server-side changing of the width is trivial.
RadScheduler1.Width = Unit.Pixel(700);
Hope this helps!