Prioritization and Shaping?

So I have a QoS policy that I've been messing around with. The policy currently uses bandwidth statements for each class.
I am wanting to modify one of the classes in such a way that this particular class can never exceed 256kbps, but when it is not being used the other classes can use it.
I have tried to nest a shaping policy within, but it would appear GTS is only allowed at the parent level.
Any suggestions?
Thanks
I am wanting to modify one of the classes in such a way that this particular class can never exceed 256kbps, but when it is not being used the other classes can use it.
I have tried to nest a shaping policy within, but it would appear GTS is only allowed at the parent level.
Any suggestions?
Thanks
Comments
On the second, yes class default can use the bandwidth if it is not being used.
One more question if you don't mind. If shaping is used in place of policing, are the other classes able to use all bandwidth if shaping class is not?