Wipe using an image?

Hiya all -

Imagine you're watching the news. In the front of many newscasts, there are teasers with wipes between. Those wipes are (usually) similar to their lower thirds, just vertical. In other words, it's not a straight line.

I've been achieving this in FCP using a regular left to right wipe, then on the above layer, making a vertical image move from left to right to cover up the wipe edge.

So is there an easier way to do this? Some transition either in FCP or available for download where I can tell it to use my image as the edge of the wipe?

Thanks for the help!