Even though it's been reported that they don't work with the 2600, I picked up an 8Bitdo Bluetooth Receiver for MegaDrive/Genesis, on the hunch I could make it work with the 2600. (my hacks were the first 2-button genesis-pad games running on the 2600. I have some familiarity with the scheme)   The reason that genesis pads work at all on the 2600, is the +5v line on the 2600 is connected to the genesis controller SELECT line, which results in two things - it selects the B and C buttons