What you want is how many firms indeed operate. in fact, the whole concept of margin kind of disappears and is replaced by in depth risk analysis.
This is a very time intensive process involving several highly paid people and isn't something you can just "sign up" for. They need to have strong indications that your commissions would cover their costs and more. At least $500k/year. Think about it, you basically want them to throw out the exchange margining system and replace it with something very customized to your position and trading style. There's a lot of inherent risk in doing that for any customer.
Sounds like your best option is to use someone with lower intraday margin. That is pretty easily done. But to hold overnight you'd have to go through what I described above.
This is a very time intensive process involving several highly paid people and isn't something you can just "sign up" for. They need to have strong indications that your commissions would cover their costs and more. At least $500k/year. Think about it, you basically want them to throw out the exchange margining system and replace it with something very customized to your position and trading style. There's a lot of inherent risk in doing that for any customer.
Sounds like your best option is to use someone with lower intraday margin. That is pretty easily done. But to hold overnight you'd have to go through what I described above.