Not really. You can find systems like the RO Buddy but they are not very good performers, end up costing you more than a normal reef quality RO/DI and aren't much smaller than a normal RO/DI anyway. With a very small reef you are probably better off buying jugs of distilled water at the grocery or RO/DI from a trusted LFS or even a reefing friend. Purchasing water is cost effective until you get a larger reef then it would be money well spent to get a real reef quality RO/DI from somewhere like Spectrapure, Buckeye Hydro or PurelyH2o.
Even a full size RO/DI can be disconnected when not in use an stuck in an out of the way closet or cabinet until next use.