Tree Fragment versus Node Set

I realize that its always better to form my variables into node-sets
versus tree fragments by using the select attribute whenever possible.
But, can one ALWAYS prevent (in XSLT 1.0) making a tree fragment? For
example, if building my variable comes from a template call, is there a
better way to do this?

   <xsl:variable name="myVar">
      <xsl:call-template name="buildMyVariableNode">
         <xsl:with-param name="arg1" select="'test1'"/>
         <xsl:with-param name="arg2" select="'test2'"/>
      </xsl:call-template>
   </xsl:variable>

-Thanks,

Kevin