Currently when you set Country on the profile page to United States or Canada, the Region filed is filled with states / provinces.  
I want the City field to be filled with cities when a region is selected.  I want to do this without modifying the core.

I created DNNCityEditControl.vb which is very similar to core DNNRegionEditControl.vb
I added City datatype and created lists of cities.

Since I don't want to modify the core I created new DNNRegionEditControl.vb where I modified the constructor to:
AutoPostBack = True (instead of the original 'false' in order for it to trigger the city control)

Now I have to add code to the ProfileEditControl.vb Protected Overrides Sub CreateEditor()
to trigger the city field when region is changed.
Currently it only triggers the region field when country is selected.
I know how to do this by modifying the core ProfileEditControl.vb but how do I do without modifying the core?
If I create a child class that extends ProfileEditControl.vb and override CreateEditor() then how do I tell the profile page to use the child class without modifying the core?
I"m lost on this one.  Any suggestions are appreciated.