I am throwing out some ideas without to much thought so bear with me.
They don't actually measure GH levels. It is too difficult. So they measure IGF-1 levels. So my theory is that you want to drop IGF-1 levels even if GH increases.
Again, I may be wrong on this, but this is how I understand it
GH + insulin + estrogen = IGF-1. I know it is more complex than this but insulin and estrogen influence IGF-1 from GH. To lower insulin go on a starvation diet. Actually your body will respond by increasing GH but it should decrease IGF-1. IGF-1 is a growth factor. When you are starving it makes no sense for your body to be in a growth state. At the same time, take l-dex to drop your estrogen levels. Maybe the two together leading up to the test will drop IGF-1 levels. Androgen also increase IGF-1 levels, so a good type would be during the recovery period after a cycle.
In addition, stop all forms of exercise a week before and get as little sleep as possible. Since the biggest spikes of GH happen during heavy exercise and during sleep.