The way I always do it is this....
just get a cheap set of headphones and cut the headphones off....you just want the cord.
Then, strip back the insulation.
Inside, you will have an 2 insulated inner wires (usually red and white) and an outer braided copper mesh that covers the insulated inner wires.
Strip the insulation from the red and white wires and twist these together. Then, twist together the outer copper mesh that covers the inner wires.
Tie these 2 leads down to the tip and ring sides of a surface mount jack, then tie down a jumper wire and punch it down to the MOH port coming out of the switch. (Or you might just scotchlok the jumper wire together with the headphone cord leads.
Either way will ensure that you hear both the right and the left channels of your stereo CD player through the mono MOH input.