Have you tried adding citric acid to thawed cum? I sometimes use this stuff labeled "sour salt", which is basically citric acid in powder form. I once added just a tiny bit to a cum shot, and it got rid of the bad taste and smell, without significantly effecting the flavor or smell to the point where it's no longer "cum". It probably works because cum is alkaline, which gives it that "bleachy" smell, and the acid neutralizes it.