Photoshop :: Control Auto-Align And Auto-Blend

I have just moved from 7.0 to CS3 (and PC to Mac) and am currently trying to get to grips with the new features! Once which I love is the auto-align and auto-blend feature(s). My question is, is there any way to control how these features work? I have seen on some web sites people talk about 'fuzziness' sliders where you can control that if an object (pixels) appear in X% of the photos they should/shouldn't be included in the final image but I cannot find these.

My intention is to use these features to take photos of monuments and have the people who are moving about removed from the final image (I guess it's the auto-align that would do this.) I tried a test and took a number of photos at home but I kept moving one object around (a pen.) The pen appears in all the images but in a different location so it always appears in the final image. When I tried auto-align with a stack that included one image without the pen, the pen was removed from the final image. Given the first scenario (i.e. the object is in all the images but in a different location) is there any way of automatically removing it using auto-align or would this have to be a manual process? In the real world, it would be possible to take a photo of a monument with people in different locations but it would be much harder (or take a long time) to take one where at least one person was not in all the photos (there's always someone loitering.)