You should try masturbating with the flu. Larry David did a stand up bit on it that is hilarious. I tried it. After about 10 minutes you are out of breath and approaching exhaustion. You are nowhere finishing, but your erection does not subside. So after you take a break you go back to work, periodically stopping to catch your breath. At 20 minutes you feel like you are going to die. Then you begin wondering if you should call your doctor. But what would you tell him? At this point you are delirious. The only way to end this torture is to finish the task, so you get back to it. Finally, at around 30 minutes you feel something start to happen, so you start furiously yanking because you know the end is near. Finally, you reach that moment and blow your load. The pain is over and now you can lie down and relax, in shame for realizing you almost killed yourself whacking off.
The point is that it takes FOREVER to blow your load when you have the flu. It is very unpleasant, but you cannot stop once you start.
Give it a whirl, Grampa, and tell us how it goes!