Note: the use of the term green here may not be in the same context as what you're thinking!
Step 1: Preparation
1x Cisco WS-C2950C-24 - 24 10/100 ports with 2 100BASE-FX uplinks, Enhanced Image
Seeds of your choice
Step 2: The Keyboard
Make sure it's well covered
Wet the paper thoroughly
Step 3: Sowing the Seed
If your mate is off for a month or more, grass seed will give a lush greenness not obtained with other seeds.
Step 4: Germination
Unpack the Catalyst switch and discard all the contents apart from the bag with the book and cables in.
Discard the the book and cables and split the bag down each of the long edges
You should end up with a rectangle of polythene, half a seal on each end, which just fits over the keyboard.
Water the seeds again, and place the polythene over the keyboard.
Note: this could work with other polythene - I didn't have any other polythene.
Step 5: Growth
Step 6: What Next?
You could surround the keyboard with gravel, place a small dish in the gravel and add Sea Monkeys to give that calming Japanese Garden with Koi Carp feel
For an English Cottage Garden feel, thimbles and fishing line can be used to make hanging baskets. Superglue them to the front of his/her monitor
Toy people and bears will recreate the fear of a wild forest on the keyboard. Use epoxy to glue them to the keys before adding the paper.
If your colleague is only off for a week, why not go for instant results with turf?