Modal operation using IMessageFilter and DoEvents

Application::AddMessageFilter(someFilter);
while(someFilter->HasUserSelectedAPoint_Or_HitEscapeKey()){
    Application::DoEvents();
}
Application::RemoveMessageFilter(someFilter);

Application::AddMessageFilter(someFilter);
while(someFilter->HasUserSelectedAPoint_Or_HitEscapeKey()){
    // Assuming that ManagedGetMessage() below is a blocking
    // call which yields control to the OS
    if(ManagedGetMessage())
        Application::DoEvents();
}
Application::RemoveMessageFilter(someFilter);