In theory the guest does not have to be on the same flight, although I don't actually know how they feel about leaving the guest there once the host has gone (I've always wondered about this - for lounges in general not just the CCR - but never had an occasion to test it out).

However, why would your friend want to spend four hours alone in the CCR? It's just a lounge. The champagne is good. The dining area is claustrophobic, the food dull and the staff clueless (at least that is not only my view, but also the view of three friends I know who have been there at separate times). The chairs are very comfy and the selection of magazines and newspapers is peerless, but there is no way I would chose to spend four hours there on my own.