I've heard it's common to add weight to the tripod head to help simulate 35mm camera movements.

Which tripods would support adding additional weight?

I read David Lynchs' crew did this using a PD150 for their PlayStation commercial.

I heard something similar was done when Allison Anders filmed 'Things behind the Sun' here in FL. They wanted the
camera kept locked down just like a traditional 35mm shoot.

It depends on how long you want your tripod to last. Smaller, lighter tripods, have only fluid effect heads. Not true fluid heads. The added weight to an already marginal head will temporarily improve its pan and tilt movements. But in very short order the head will need to be replaced. This is a good trick for short term projects, like several weeks of shooting a feature. But most of the modestly priced heads need to be kept within the manufactures guidelines for camera weight. Heads built for heavier duty will handle the temporary stress of heavier loads better. If damaged, the heads can be rebuilt. Lighter duty heads can be replaced for the cost of rebuilding the head.

Jeff