Theme for only one network site

Here's my dilemma: I, the super-admin of my BP/multisite install, have created a network site specifically for use by the community. I need to assign a special theme to it, with includes special functions; but I do *not* want this theme available to other network sites, only this one network site I have created myself. Does anyone know how I can do this - make a theme available to one site on the network, but not for any others? My thanks in advance --