Add pepper to the coffee supply.
Pepper naturally follows salt. If you are adding salt to the sugar supply, you can also add pepper to the coffee. This prank only works with large portions of ground coffee. If individual packets of coffee are used to make a pot, try adding the pepper to the water reservoir. No one ever checks or cleans the water reservoir in the office coffee maker. If you want a scare, take a look inside the chamber.
If possible find other places to hide pepper in the work environment. Look for places that may release the pepper into the air, thus reaching a target. For example, sprinkle pepper on boxes that are stored on high shelves. People often tip boxes toward themselves when taking down. This should let the pepper cascade down onto their face. Unintended sneezing fits may ensue.
Other places pepper enjoys a home include, hats, coats and ceiling fans. If the fans are turned off, place pepper on the blades as wait for a pepper bomb once the blades are turned on. No one will know exactly where it is coming from.
Just like your salt related pranks, you may wish to test run your mixes at home before unleashing on the office.