Try an exercise ball that matches your height. If its extremely difficult, start at your waist. With the ball under your waist, your hands on floor in the pushup position. Do as many as you can for a few days, or until you know its too easy at that stage. Then move down to thighs, knees, then ankles. The ankles are the hardest. When you can do 9 at the ankles, the floor should be no problem. Unforunately you cannot do your pushups at the knees during the test, yes it would be easier, but I tell you doing it the "man" way is such an accomplishment. It took me about a month in a half to do one. When I took my test last Aug I was able to do 11, & I was so nervous to do 9. I tell you all that hard work paid off,I felt fantastic. Oh & just to tell you I originally decided to join the CF in Sept 2002, but did not put in my application until Feb 2003, just because of the difficulty with the pushups.
Good Luck!
Kris