To make it look as if you had a protracted illness:
Wear clothes borrowed from an overweight friend to give the impression that you have lost several pounds. Note: If you are overweight yourself, wear figure-controlling underwear, unless you have a friend even bigger than you are.
Smear purple eyeshadow under your eyes.
Faint every time you stand up. Conversely, manage to walk halfway across the office on occasion and faint in mid walk.
Buy several Get Well Soon cards, write them to yourself from friends and relatives and stand them up on your desk.
Ask your mother to telephone your boss every couple of hours to check that you are all right. For good measure, ask her to tell him: "We almost lost him/her, you know."
To convince him you're still sick:
Walk in carrying twenty boxes of tissues.
Raid the medicine cabinet for those not-quite-finished prescription pill bottles and line them up on your desk. Set a kitchen timer to go off every few hours and pretend to take them. For good measure, unscrew a lid every time the boss walks past.
Hire a nurse from an agency and take her to work with you. Her brief is to take your pulse/temperature/blood pressure at regular intervals.
Hire an ambulance and get them to park outside your place of work - on standby. You might like to try this with a hearse.
Groan loudly every few minutes. This is particularly effective when speaking to customers/clients in person or on the telephone.
To substantiate a physical injury:
Make a plaster cast by soaking kitchen paper in flour and water paste and wrapping round a limb. You will need to do this the night before.
Limp everywhere. Note: Make sure you remember to favour the correct leg when you do this.
To guarantee being sent straight back home:
Stick those adhesive reinforcing rings all over any areas of exposed skin, to make it look as if you have some exotic tropical illness.
Be overheard saying to a colleague "Is bubonic plague contagious, do you know?"
Periodically have a violent retching session. This works particularly well if you can manage to secrete a container of vegetable soup about your person and spill some on the desk when no-one is looking.
~ problems solved ~