buffer nodes before last tweaked node

In order to speed up compositing I would like to suggest the ability to temporarily create a buffer of the nodes prior to the latest changed node(s).

In this example image, Mario is put on top of a background image that is blurred multiple times. When I change the transform (marked BLUE) of mario, the compositor will recalculate each blur node of the background (marked RED), which takes quite some time. If the nodes marked RED would had been temporary buffered, only the nodes marked GREEN would need to be recalculated. This would require some additional memory for the buffer, but make compositing render times much faster!