How to store 'home notional salary' for International Assignees?

Summary:

When employees go on an international assignment, we terminate the home assignment and create a new host assignment. Their salary and any other relevant elements are added to the new host record and salary increases are managed on this active assignment. We have been asked whether it is possible to track the 'home notional salary' in HCM rather than on a spreadsheet - this salary would keep pace with any increases processed on the host record but is purely for informational purposes and would be reviewed if/when the employee returns home. We, obviously, can't track the notional