Computed value shown in CMS Editor

My scenario is rather simple:

I'd like to have a Page property that is automatically calculated (e.g. hashcode). I tried to achieve this by several ways but with no success, i.e.:

• By having calculation in property getter and return value, like: get { return HashCode(); }
• By using GetPropertyValue with default value.
• By setting SetPropertyValue in getter and then use GetPropertyValue.
• I had a mix combination of setter, i.e. empty setter and SetPropertyValue.

None of the above works fine, i.e. CMS Editor does not show calculated property. It's just an empty field.

What's the recommended way to achieve that?