[XeTeX] Lucida Sans tracked tighter

[Robert Spence]

On the Gentium project page at SIL International
http://scripts.sil.org/cms/scripts/page.php? 
site_id=nrsi&id=Gentium_status
it says:
"There have also been requests for a complementary sans-serif face.  
(...) Lucida Sans, tracked a little tighter, works well."

Can anyone tell me if there's a way of doing this with XeTeX and the  
preinstalled version of Lucida Sans that comes with Mac OS X Tiger?   
I can see what the result would look like by typing some text in  
Lucida Sans into TextEdit then selecting Format > Font > Kern >  
Tighten.  But if I XeTeX AAT-info.tex and OpenType-info.tex for  
Lucida Sans, no features show up of the kind that fontspec.sty might  
be able to use for achieving this effect (as far as I understand  
it).  I've tried Skia in various weights and widths as a sans serif  
companion for Gentium, but the result was somehow always subliminally  
too impudent.  This is a real aesthetic dilemma.

Grateful even for negative responses,
and hoping this isn't going to spark off another heated debate about  
font licenses
:-(

-- Robert Spence
Applied Linguistics
Saarland University
Germany