No attachment, the weight of the scion is all that is needed from seedlings. The stock hardly grows at all, what you see in that pic is pretty much wat you get at the end but with a much larger scion.
The only problem I had when starting out with this stock was too much humidity. Hylo are really rot resistant, the nice thick green skin is what achieves the great resistance. When you cut the skin they become susceptible to bacteria, so just be careful and regulate the humidity.
Apart from that it's straight forward much like pereskiopsis.
Let us know how you go with them. When are you planning on grafting ?