What are the biggest barriers for you with regards to doing this test?
Specific fatigue/weakness issues?
Systemic fatigue/weakness issues?
Have you ever had swimming/running instruction? Do you think you could clean up/improve your technique if you did?
Have you thought about adding weight/resistance to both your push ups and your pull ups? This may give you enough boost to power through more reps.
What is the timeframe on this?