Actually, although I agree that all the protocol books (Maniatis, etc.) do say that this must be prepared fresh, I don't think it's required.
I mean, most (all?) plasmid mini- and midi-prep kits from Qiagen, Promega, Invitrogen, et al. rely on a straight forward Birnboim & Dolly alkaline lysis procedure; the only modification is column-based recovery rather than precipitation. These kits sit in a warehouse or two before they arrive at the lab, then sit on your lab shelf while you use them up, and there's no problem with the NaOH/SDS solution...