Instead of removing the radiator cap can't you just replace it with a really high rated pressure?
What we did was to run a cap on the radiator that has no pressure spring on it so the fluid passes through the overflow outlet/inlet as it needs to, then you put the pressure cap on the overflow tank with a line going from it down to the ground, or an overflow bottle, but it really shouldn't overflow from there. You then fill up the radiator through the expansion tank, which is why you want the cap to be higher than the radiator. This system is similar to a remote res on a shock, it allows the radiator to always be full with water and has extra in the res. to make sure air is never introduced into the radiator...
