It helps if before there is a problem you accuse them of mental instability and create a culture of bias and ostracism and lighten their workload. Prevent them from participating in any way with the running of the company. Send them on wild goose chases. Assign them things that do very little and will never see the light of day. This has the double effect of giving them more time to worry about the immense workload that is being neglected and making them look useless. If they weren't crazy before they sure will be in a few months when the pressure to meet deadlines builds and they are unable to do anything about it.
IANAL but that would make it even worse, and likely lead to a lawsuit. Hostile work environment, or discrimination based on medical condition would be actionable.
