Using item data with constraints

I would like to display a combo box within a CXTPPropertyGridItem and I would like to associate some item data (e.g., DWORD or void*) with each item I add to the combobox list. I presumed I should use GetConstraints() and AddConstraint(), but I can not find any way to associate item data with a constraint. I could maintain my own array of item data and map the constraint index to the index in the array, but if the constraints are sorted I assume the indices will become out of sync with my member array.

With an MFC CComboBox I would simply use SetItemData()/SetItemDataPtr(), but I can not find any like this at all with the propery grid. Does anyone know how I can do this? Is there a completely different approach I need to take for the property grid item? I have been unable to figure this out looking through the samples, help, and forums.