Add a circuit into electrostatics module in the form of weak form instead of use cir module

Hello everyone,

Recently I am working on a PZT device, which has a cir shunt. I need to do a eigenfrequency analysis of this device. But cir module does not support eigenvalue solver. As I know one of the way is use weak form to include the cir impedance as a boundary condition. But I can not figure it out how to add impedance in the weak form in the es module. Does anyone has relevant experience or any ideas?

Thank for your reply. Best, Sam