Futures Broker - Interest Question?

Hi folks, I am looking for a futures broker that will pay me interest on my funds that are not in use. Seeing that I will have at most 10% of my account in trades at a given time, this becomes quite a waste if not getting my just earnings. I have contacted three brokers and they have all said they do not pay nor will negotiate a rate with me. I do not understand this, considering my stock broker doesn't seem to have any trouble paying me 3.5% (fair enough).

Could someone give me direction?

Thanks

I know interactive brokers do pay interest to larger accounts.

Some brokers accept T-Bills as margin collateral instead of cash, but that is subject to negotiation (i know IB does it for >1mio accounts, also MBTrading is willing to talk, dunno about others).
BTW, many bokers hold their clientfunds in T-Bills, they are basically as liquid as cash and brokers make a chunk of money on it, by crediting no or bad interest on account balances.