This describes what is the opposite of what is needed for both systems. Why do you need this capability?
One option is to copy the data into global fields for each user via script. Then the changes made to the global fields will not be visible to the other user. To "save" your data, a script would then copy the data from the global fields back to the original fields of the original record. If two users were to try to do this at the same time for the same record, there may be problems due to an edit lock on the record from one user preventing the "save" from taking place from the other user's global fields.