You can make a reflector out of foil and use double-sided tape to get it to stay put. Basically you take a piece of foil, fold a couple of times (but make sure it doesn't get too thick that your bulb can't fit once it's in place), and then place it so that it rounds over the bulb with about an inch or two on both the top and bottom. Repeat as necessary to fit the length of your fixture. From what I have read, it's not as effective as "real" reflectors, but it's more effective than having no reflector.