Hi there,
Unfortunately I don't think there is very much you can do. The insurer needs to know who the registered owner is for that exact reason... to load or award depending on who it is.
There's not a way round it as far as I can tell.
Perhaps the leasing company have some insurers that they deal with on a regular basis? You will still be eligible for the usual insurer/broker discounts, providing you meet their criteria, as the keeper/owner isn't an issue in this respect.