WiX 3.7: How to add or update a dialog during uninstall?

WiX 3.7: How to add or update a dialog during uninstall?

I need to add a dialog box that would pop up during complete uninstall
(not major upgrade) right after the confirmation ("Are you sure you want
to uninstall this product?") dialog. This dialog would prompt the user to
answer a question and based on the response, set up a property that would
be used in the condition for the RemoveRegistryKey element (i.e. it will
remove a registry key only if the user selects an option to delete the
key).
I have an idea how to add a dialog to the install sequence (I am using a
modified WixUI_InstalLDir sequence to which I added a custom dialog I need
during installation), but I can't find any references that would explain
how to add a custom dialog to an uninstall sequence. It would be even
better if I could modify the uninstall confirmation dialog, so the user
would see one dialog instead of two. An the key thing would be to be able
to set up a property that could be used in the component condition.
Is this possible? Are there any examples how to do this?