Apply button on wxDialog

I would like to be able to add an Apply button to a Dialog so that it
triggers the validation of the TextCtrl widgets in the dialog (like the OK
button does) and then, if the validation succeeds, it calls my own function.

If I just add a button with it's id set to wx.ID_APPLY, the validation and
transfer functions appear to be called, but I can't find a way to hook in my
own function call on success.

I see in the wxWidgets documentation that the wxDialog class has an
OnApply() method, but this doesn't appear to be exported to wxPython.
However, the C++ method returns void so I wouldn't just be able to call it
anyway.

The OnApply() method calls wxWindowBase class methods Validate() and
TransferDataFromWindow() - being able to call these from wxPython should do
the trick - is that possible? or is there a simpler way to do it?

Using wxPython-2.5.1/Python-2.3.3/Windows2000

regards,
Richard