Not a good idea.
The ribbed design of the Castle motors does not lend itself to heatsinks.
For a heatsink to work it has to have as much contact as possible with both air and the object it's transferring the heat from.
The contact area of the castle motors is to small for a heatsink to work properly.
Istead the air would be trapped between the ribs and still standing air does not transfer any heat.
Adding a heatsink to a castle 2200kv would most likely cause its temperature to rise.