Try something like this:
Use Translational Mechanical Converter for each domain, connect the R port, and add a small mass. Reverse the orientation in the dialog box for the gas one (IMPORTANT!!). That's pretty much a gas charged accumulator. The two fluid chambers will almost always have the same pressure. If you would like to the temperature to be linked as well, you may connect the H ports via a small thermal resistance. You can add a spring and/damper to the R port if your component has one.
