Most water conditioners will also treat chloramine, but check on this with whatever water conditioner you are using.
Water conditioners that treat chloramine do this by breaking the chemical bond in the chloramine into chlorine and ammonia. The water conditioner will then treat the chlorine leaving the ammonia which under normal circumstances is processed out by the nitrogen cycle.
So you are correct that this makes fish in cycles using chloramine treated water more problematic. However you can absolutely still do a fish in cycle with chloramine treated water. 0.3ppm ammonia is essentially zero and of no risk of harm to fish. While this ammonia will be in addition to whatever your fish produce, you can still maintain safe water parameters through regular water changes. Might be a bit more work but you can do it. Also some water conditioners like prime will detoxify the ammonia for a couple of days so this gives you a safety net too.
Many people keep fish in chloramine treated tap water, and i would expect most of those did fish in cycles.