Column variable

This is my region body statement:

<fo:region-body margin=".9cm" column-count="4" column-gap=".1cm"/>

This is my region body definition:

<fo:flow flow-name="xsl-region-body">
	<fo:table>
            <fo:table-column column-width="3.5cm"/>
            <fo:table-column column-width="2.5cm"/>
            <fo:table-column column-width="1cm"/>
            <fo:table-body>
		    <xsl:apply-templates select="Cont"/>
            </fo:table-body>
      </fo:table>
</fo:flow>

Is there a variable that would let me know which column I'm in (of the 4
region-body columns - not the table columns)?

I am trying to figure out a way to have varying spacing between the 4
columns.  I would like to do this by varying the width of the last
column in the table (it's an empty column).

For example, something like:

<fo:table-column column-width="(((column_number() mod 4) mod 3 - 1)*2 +
1)cm"/>

Would give me a 3cm gap between the 2nd and 3rd column and a 1cm gap
between the other columns.