setting a particular table's column widths with xsl

Hi again all,
    I've got a particular type of table that I want to set column widths 
on via xsl rather than having to do it in the xml source.

The reason is that I have _lots_ of xml files that will use this type of 
table and I don't want to have to maintain this if/when we change the 
table layout.

The html is easy with the css.
I'm having a problem with the pdf/ps output.

I don't want to have to use 'colwidth' like this:
<informaltable tabstyle='encoding'>
   <tgroup cols='4' align='left'>
     <colspec colname='c1'  colwidth="1.0*"/>
     <colspec colname='c2'  colwidth="3.0*"/>
     <colspec colname='c3'  colwidth="2.0*"/>
     <colspec colname='c4'  colwidth="3.0*"/>
     <thead>
       <row>
...

I want to be able to just do:
<informaltable tabstyle='encoding'>
   <tgroup cols='4' align='left'>
     <colspec colname='c1'/>
     <colspec colname='c2'/>
     <colspec colname='c3'/>
     <colspec colname='c4'/>

   <thead>
     <trow>
...


I cant' figure out how to do this.
I've seen examples on using the table.layout template and such but I'm 
not having any luck.

IE:
<xsl:template name="table.layout">
   <xsl:param name="table.content"/>
   <fo:table width="100%" table-layout="fixed" column-width="1.0">
     <fo:table-column column-width="proportional-column-width(1.0)"/>
     <fo:table-column/>
     <fo:table-column column-width="proportional-column-width(1.0)"/>
     <fo:table-column/>
...


Can someone point me in the right direction?
thanks,
marcoz