So, just choose a bond as pointed out by def and create an order and check margin impact without submitting the order. Easy enough, no?
I guess I'm giving up, this is as useless as calling customer service.
My question was: "I am looking for EUR denominated government bonds or any other instruments that can serve as futures collateral in lieu of cash (similar to U.S. T-bills), to avoid having a too high cash drag in the futures segment of the account, as IB pays 0% interest on cash-based futures maintenance margin. Thanks for looking into this."