As far as I can understand, you do not want to have a particular property (IsReadOnly in this case) displayed in the property grid. If that is so, you can try handling AutoGeneratingPropertyDefinition and cancel the generation of a particular property.
void propertyGrid_AutoGeneratingPropertyDefinition(object sender, Telerik.Windows.Controls.Data.PropertyGrid.AutoGeneratingPropertyDefinitionEventArgs e)
if (e.PropertyDefinition.DisplayName == "IsReadOnly")
e.Cancel = true;
Is that the behavior you are looking for ?
the Telerik team