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Questions about dc bias current return path in AD623

Hi everyone,

I want to use AD623 to do the first stage of a large gain multistage amplifier circuit(G = 200~1000). The voltage of my input signal is about 1mV, so i need to remove the dc bias current. If i series 1nF capacitors  at the input of AD623, which will not work because of no dc current return path.But I don't want to use parallel resistance because it can reduce input impedance. I want to keep the input impedance  about 2G Ω. And i also don't want to use inductors in my circuit. The frequency response is about 50HZ of high pass filter. Is there any way i can filter out the dc bias and keep the input impedance constant about 2G Ω? By the way,  it's OK in multisim that i series capacitors at the input of AD623, but in the fact that AD623 can't work because no dc current return path in my experience.

Very grateful for your help