Castle Quick Connect and Quick Connect Duo do just that. They detect the presence of a Castle Link adapter on the free lead and switch the controller's signal line from the receiver to the Castle Link. Easy as that.
Follow the applicable Connection Diagram (found on the inside of the package or the link below) when connecting the Quick Connect or Quick Connect Duo. Don't forget to use the included piece of heat shrink tube to secure the ESC lead to the Quick Connect.
Quick Connect Duo supports all Castle Link capable ESCs but is designed specifically for use with Castle ESCs featuring AUX wire technology.
Note: Neither Quick Connect, nor Quick Connect Duo will work with the Field Programming Cards when used as a standalone programmer. It will ONLY work when using the Field Programming Card as a Castle Link adapter.