Yes, I think you can solve this.
In your XML package used to display the product, you can check which position you are displaying for each product. When the position is exactly divisible by 4 (the right column), change the CSS class to not show a right border.
It's difficult to explain without your code but something like this...
If your regular display was this:
Code:
<div class="has_a_border">
your product goes here
</div>
...and no right border was
Code:
<div class="no_right_border">
your product goes here
</div>
Then the XML package code could look like this:
Code:
<div>
<xsl:attribute name="class">
<xsl:choose>
<xsl:when test=position() mod 4 = 0>no_right_border</xsl:when>
<xsl:otherwise>has_a_border</xsl:otherwise>
</xsl:choose>
</xsl:attribute>
Your product goes here
</div>