Make two labels like normal. One to be the "container" which will appear as the bottom label. Make another to be the label that goes inside the container label. Lets say the container (aka parent) is named Big, and the label that's going in to the container is named Boobies (aka the child). Your hook line will look like:

*BigModuleHook !LabelLsBoxHook Boobies

Then, you have to keep in mind, that the x/y coords to position Boobies, inside of Big, is relative to Big's top/left corner (which Boobies will see as 0/0 - so if you give Boobies x/y coords of 10x/10y, it'll be 10px off of Big's top/left).