Retro game hardware manufacturer AnalogueNT has created the Retro Receiver, a $20 accessory that behaves like a BlueTooth receiver. The Retro Receiver allows you to connect wireless controllers to the Nintendo Entertainment System or AnalogueNT without any internal modification.
The Retro Receiver is a collaboration between AnalogueNT and retro-inspired controller manufacturer 8bitDo. Because of this, all of 8BitDo’s Bluetooth controllers are compatible with the Retro Receiver. However, there is also support for all PS3, PS4, Wiimote, and Wii U Pro controllers. If you wish to purchase the product, you can do so here.