Why not just get your buddy to loan you his trainer for enough flights to convince your instructor that you're ready to fly?

When you say you flew the trainer, and it was a joke, what did you do? Did you execute the complete takeoff and landing maneuver? Did you grease your landing? Can you do it without someone reminding you how to set it up? Did you execute any stalls? Spins? Rolls? Did you fly it inverted? Can you do an inverted figure 8?

These are all maneuvers you should try to learn. The trainer will give you a much larger margin of error than an aerobatic or 3D plane will.

The true test of your flying ability is not whether you trust yourself to fly your plane, but whether your friends trust you to fly theirs.

Brad