Personally, I would not house a fish in a QT. I don't think it is right to be continueously exposing fish to meds and treatments. Additionally, ideally, except with schooling fish, or mated pairs, QT's should only house 1 fish at a time.
You can keep the tank cycled by feeding the tank with fish food. I don't bother doing this myself, as I don't usually make impulse acquisitions. Before I plan to get a fish, I'll spend some time "reconditioning" the QT.