If you really need huge number of micropaiements per client per day, I'd suggest you to use a different paiement system.
You could use an account-based paiement system. Optionnaly this could use David Chaum's e-cash system if you want anonymity.
Anyway, your clients would have an account on your server, and they could change their balance into bitcoin when it reaches a significtive amount, or on a daily basis.
I guess I'd like another requirement on this sub-net too: It should be peer-to-peer and not a centralized solution. Yes, a central server could perform this kind of system with all of the headaches and problems that such a solution also provides. I would personally like to avoid having to turn Bitcoins into a conventional client-server model with a central authority which can be attacked. It goes against the grain of why Bitcoins was originally established.
Bitcoins itself could be built into a central server system too, but I perceive the peer to peer nature of Bitcoins to be an essential strength of the system and something to be modeled onto sub-nets too.