qt creator promoted widgets dialog

i have a derived QMDiArea which contains some additional functionality over and above the base class and i wanted to promote the existing mdi area to this derived class. the promoted widgets dialog contains a list of available base classes and QMdiArea is not one of them. is this an oversight or is there someway for me to add this to the list?

thanks

i found a workaround. i promoted from QWidget then i deleted the mdi area and then put a widget there which i named as mdiArea so that it can be refrerred as ui->mdiArea in code. i then promoted this widget to my derived QMdiArea and when it compiles all works just like i wanted.