Window -> Libraries

You have to open it when you're in the setup room as it is not opened by default. 

Once it is opened, with your object-to-be-rigged selected, navigate to your folder with V4 in it and load her in. It will bring up a hierarchy menu that has a box that is checked that says Auto Groups, leave that checked (unless you already have the groups defined, then uncheck it). Scroll through the hierarchy and uncheck all the body parts you don't need added to your rig. Then press OK. The object will be rigged and you can exit the setup room. 

Then you can go about adjusting things, adding morphs or magnets etc, so that there is minimal poke-thru when posing. That is, assuming you're trying to rig a piece of clothing. 

ETA: Once back in the Pose room, with your new piece of clothing selected, you can go to FIgure ->Copy Morphs From... and select V4. Same with joint zones - Figure ->Copy Jointszones From... (right below copy morphs from), but you don't really need to do that. I do it anyway just for safe measure.