Apply the tester and then turn the engine toward TDC with a wrench, you probably won't be able to get to TDC but you will cover the ports. The only thing that this will not test is if you have a lot of taper in the cylinder.
One BIG warning, DO NOT position the engine at TDC and then apply the tester, the odds of being at EXACTLY TDC are infinitesimally small and things are going to fly.