AE CS4 - Render Only Effect?

Let's say I have a layer that is a solid color background (such as black or purple or whatever).  And I add a Lensflare effect to that layer in the center of the frame.

If I render this out... what I get is a black background with a lensflare (naturally).  But what I would like is to render and only have the lensflare... not the background.

Is this possible?

Thanks!