Would be easier to bind the IsChecked property to a public property to handle this situation.
For example:
private bool _cbIsChecked;
public bool CbIsChecked
{
get{return _cbIsChecked;}
set{_cbIsChecked = value;}
}
Then you should define a method where this property is been set.
Don't forget to implement the INotifyPropertyChanged, so the UI refreshes itself.
Raise it in the set of the public property.
For any further questions, just ask.
Hope it helps :)