You make the rule that people should be referred to by their handles.
I don't think that special rules for each person is a good idea. It's complicated and it confuses people about what the rules (in absence of a special rule) are.
And anyhow, if there is a special rule for someone, then you should be the only one to communicate it. People should not be able to opt out of rules on their own (non-Robert) say-so.
If Tom wants to be called Tom, then there is a much easier solution than having a special rule for him. He should just use the handle "Tom".