[Radiant] <r:navigation> Accessing Page Parts

[Phillippe]

I have been fighting with creating a navigation which accesses a page 
part from the looped list of urls rather than the usual <r:title>, 
<r:url> ...

So instead of using <r:title> I have created a page part named alt_title 
and have tried accessing it as you normally would: <r:content 
part="alt_title" /> but within the navigation tags:

<r:navigation urls="Home:/; History:/about/history/; About:/about/; 
Services:/services/">
   <r:normal><a href="<r:url />" title="<r:title />"><r:content 
part="alt_title" /></a></r:normal>
   <r:here><strong>&#187; <r:content part="alt_title" /></strong></r:here>
   <r:selected><a href="<r:url />" title="<r:title />" 
class="parent"><r:content part="alt_title" /></a></r:selected>
</r:navigation>

All I get in place of <r:content part="alt_title" /> is the current 
pages alt_title and not that of the pages that are being linked in the 
navigation.

Is there any way to access page parts rather than just the main 
<r:title>, <r:slug>, et al?