CarpeTools [Design]> Create> Irregular> Selection Gradient...
Selection Gradient is used to create a gradient only on the selected patterns of the design. It creates a gradient from the center of the selection. It also replaces the design on the active layer. You can specify the size and no of steps of the gradient.

Simple Example of Selection Gradient.

Selection Gradient controller.

Original design (left), same design after applying selection gradient (right)