Formal title positioning question (XSL-FO/PDF)

Hi all!

I have a question regarding formal titles in XSL-FO output.

At work we use a DocBook setup where formal titles (in tables, figures 
etc) are positioned below the formal object.

One of the users asked if it is possiple to arrange these titles such 
that they are centered if they are only one line long but left-aligned 
if they are more than one line long.

And yes, I do know that the stylesheets have no way of calculating 
line lengths :-)

A quick hack would be to use role on the title elements to hint that a 
title is short and then customize formal.object.heading, but I am not 
quite happy with that!

Are there any clever ways of doing such a thing with XSL-FO 
elments/attributes?

Hope I made myself clear :-)

Version numbers:
DocBook DTD: 4.3
Stylesheets: 1.65.1
XSLT-processor: xsltproc
FO-processor: XEP 3.8.1

TIA!

Best regards,

	Rune Lausen