Hello, I installed 4 WeMo switches yesterday but one of my old switches only had 2 wires plus the ground. I found online a solution that somebody else used and it worked for me too.
First black to the black wire from the wall, second black with the white wire from the wall and the green and white from WeMo, to the ground in the wall.
It works well with led dimmable bulb or with the old spiral economical bulbs.
I am still testing it and checking if it gets hot or there are any weird signs. Everything looks great after 24 hours, there is no flicker.
Please let me know if I should expect any issues from this setup.