since you can't do ladybugs in the office, definitely soap spray. Try alternating every other day between these and you have to spray EVERYDAY or they'll multiply faster than you can kill them.
Day 1: A tablespoon of oil (olive oil is fine, find Neem oil if possible) and 2-3 drops of dish soap, half liter of water, shake well
-This dishsoap breaks up the oil and allows it to dissolve into the water better, it coats the aphids with a light coat of oil, and for an easy way to put it, clogs the aphids pores in there skin which is crucial to their survival, and the exposed aphids will die quickly within a day or less
Day2: A tablespoon of dishsoap with a few drops of oil (same recipe just backwards), half liter of water, shake well
-Basically this will dry out the aphids. suck the moisture from their bodies, and they will die within a day or less
Day3: repeat day 1
Day4: repeat day 2
etc etc
Neem oil is a natural defense for aphids, so if you can find some neem oil it will work even better, but olive oil is a cheap subsitute, might not kill them as fast as a day, but the trick is to do it everyday relentlessly, and make sure you get the undersides of leaves, flowers EVERYTHING, after a week or two they should all be dead, but you can still spray once a week or so for maintenance in case a couple boogers are still hiding like bin Laden