If you are trying to project onto an odd shaped screen, look into the Eiki line. They have a "warp and blend" board that you can get for them. This is a separate internal card with a DVI input on it. They have custom software where you can create the effect.
Do not stick ANYTHING to any
lens. This is very bad and the optical karma gods will smite you with hours of trying to get the glue off of the glass.
Other then that, your best bet is to figure out the shape and edit your media with a "mask" of the shape. You can create a power point slide master or an overlay in your video editing software. I have done lots of shows where we run multiple synced media or masks or whatever. If you are really concerned with light leaks, they make a "doughnut" type device that mounts about 6" in front of the lens.
Overall, you really need to look at the type of projection system you are using and test, test, test well in advance in case something doesn't work.
kw