The paper plate idea is actually pretty good. I imagine it would go something like this:
1. get a paper plate and line it with mylar
2. Make a radial cut (i.e. a straight cut from the perimeter to the centre
3. Fold one of the newly cut edges under the other forming a cone. The height of the cone increases (and becomes narrower) as you increase the overlap.
4. After you have determined the right amount of overlap, faster the edges together with glue, tape, stapes, etc.
5. cut a 2" or so hold from the top (point edge) of the cone.
6. From this newly created hole, make 4 equally spaced 1" incisions so you have 4 flaps. You can then try to push the bulb base (the socket and ballast) so that it fits sug against the ballast of the CFL. If it does not, increase the length of the 4 incisions made earlier. Iterate that until it fits snug and reinforce with tape on the CFL if you like.
Shit, I like that. I think I am going to try that myself. I just got 6 plastic beer cups that I was going to line with mylar, but I think making one out of a paper plate would be better because of the angle of the paper plate idea. In any case, mylar is 99% reflective so multiple angle bounces of light don't lead to too much loss, but the paper plate would be more directive I imagine.