SimpleList is designed to give you a list very simply. My standard line is that for somethng like this, your usage is no longer Simple, and you'll want to use TreeView and ListStore directly.
To hook into the change of the checkbutton, you need to connect to the "toggled" signal of the CellRendererToggle for the appropiate column. This is something you do as part of setting up editable cells. If you look at the source of SimpleList, you'll see in the setup that the CellRendererToggle's "toggle" signal is set up to modify the model when toggled. You'll need to fetch the cellrenderers for the column and connect your own signal handler.
... Or just create the view for yourself and you'll have the CellRenderer.
This isn't really a perl issue at all, it's just a gtk+ thing.