Uncovering a title in motion

I'd like to reveal a title with a light effect in Motion (3). As my skills are rather limited, here's what I tried. I have the title (which is an imported png) on a layer and I'm using the lens flare effect which pans across the screen left to right on another layer. In its trail the title is supposed to gradually appear.

Initally, my idea was to simply animate the crop of the title and follow the lens flare, but the crop does not offer feathering, so it looks silly. I now have an image mask with a rounded rectangle which offers nice feathering but does not appear to let me change its dimensions as the lens flare pans across the screen.

So either I'm not using the image mask the way I'm supposed to or I have some other misconception. Any simple fix for this?

Thanks,
Stefan

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macpro 2x3 ghz dual core intel, 10.6.8, FCS 2

Why was the topic moved to LA-X? I thought all things FCS2 belong in FCP. Sorry...

Stefan

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macpro 2x3 ghz dual core intel, 10.6.8, FCS 2

Oh sorry, that was me. I thought it was Motion 4 - got the versions mixed up. Moving it back now.