Hi Jay,
If you can remove the back of the projector, and if it has speed pots, you can point the video camera at the film screen whilst running the 8mm film and adjust the speed of the projector until the flicker goes away on the video camera monitor. If your camera has a cmos there will be a ghost bar slowly travelling up or down the image, (since the units aren't locked it won't stay in one place long), but it will only be noticable during low density/washed out scenes.
Failing speed pots you can cut a dimmer switch right into the power cord of the projector. Best if the projector has one of the universal power cords like for computers, as then you won't wrecking anything integral to it. It's a hacky solution but super cheap and it works. Obviously you have to set the projector to 24fps and dim down. If it won't quite dim/slow down to 20fps, try jamming the speed selector between 18 and 24fps - that will reduce the "start speed" before dimming. This last may not work on all projectors.
Then again, 24p might work :)
HTH,
Mitch