Is it possible to make a PropertyGrid property ReadOnly unless edited with a custom dialog?

Question

I have a PropertyGrid whose SelectedObject value points to a class with several members like this one:

[Editor(typeof(OutputFormatTypeEditor), typeof(UITypeEditor)), ReadOnly(true)]
public String OutputFormat { get; set; }

With ReadOnly set to true, the user cannot touch the property, even when it is being edited with the OutputFormatTypeEditor.

I would like to have it so that the user cannot directly edit the property in the property grid, but is able to when they click the little .. button to bring up the editor dialog. Is this possible? Thank you