Well, looks like you have the right idea for the SetParent API. In all honesty, I've never tried adding controls to a list view or anything else that has multiple places to put them (aside from a toolbar, but that's slightly different).
You might try to find a way to address subItem2's handle. Every control in Windows has a control (or atleast has the opportunity to apply for one). If you want to think about it in a very basic concept, imagine everything is a picturebox, except not everything has a Picture property. From there, you can see that everything has a Height, Width, and Handle. Beyond that, the controls just add their own properties as needed.
So if you can find a way to retrieve subItem2's hWnd, then you should be in business.