User address fields missing in core xml file - how can we add them without hacking core files?

Hi

I noticed in the database in the table #__payplans_user there are dedicated fields for address, state,city, country and zip code. But I couldn't find any way to "activate" them, besides adding the fields to the user.xml file in components/com_payplans/libraries/model/xml

This is the normal file

<?xml version="1.0" encoding="UTF-8"?>

<form>

	<fieldset name="addressdetails">

		<field 	name="country" 

				type="xicountry" 

				option_none="true"

				label="COM_PAYPLANS_USER_EDIT_USER_COUNTRY" />

	</fieldset>

 <fields name="params">

	<fieldset name="params">

		<field					

			name="user_notes"	

			label="COM_PAYPLANS_USER_PREFERENCE_NOTES_LABEL"

			description="COM_PAYPLANS_USER_PREFERENCE_NOTES_DESC"

			type="textarea"

			rows="3" cols="30"

			default=""

			/>



	</fieldset>

 </fields>

</form>

When modified to look like this, I could access and store information in these dedicated fields

<?xml version="1.0" encoding="UTF-8"?>

<form>

	<fieldset name="addressdetails">

		<field 	name="address" 

				type="xiaddress" 

				option_none="true"

				label="COM_PAYPLANS_USER_EDIT_USER_ADDRESS" />

		<field 	name="state" 

				type="xistate" 

				option_none="true"

				label="COM_PAYPLANS_USER_EDIT_USER_STATE" />

		<field 	name="zipcode" 

				type="xizipcode" 

				option_none="true"

				label="COM_PAYPLANS_USER_EDIT_USER_ZIPCODE" />

		<field 	name="city" 

				type="xicity" 

				option_none="true"

				label="COM_PAYPLANS_USER_EDIT_USER_CITY" />

		<field 	name="country" 

				type="xicountry" 

				option_none="true"

				label="COM_PAYPLANS_USER_EDIT_USER_COUNTRY" />

		

	</fieldset>

 <fields name="params">

	<fieldset name="params">

		<field					

			name="user_notes"	

			label="COM_PAYPLANS_USER_PREFERENCE_NOTES_LABEL"

			description="COM_PAYPLANS_USER_PREFERENCE_NOTES_DESC"

			type="textarea"

			rows="3" cols="30"

			default=""

			/>



	</fieldset>

 </fields>

</form>

So out of the box, only country field is available - why? How can we access and use these fields without modifying core files?