Is it possible to make xsl:analyze-string return one string instead of a sequence of strings?

Background: I'd like to use xsl:analyze-string in a xsl:function that should encapsulate the pattern matching. Ideally, the function should return an xs:string to be used as sort criteria in an xsl:sort element.

At the moment, i have to apply string-join() on every result of the function call since xsl:analyze-string returns a sequence of strings, and xsl:sort doesn't accept such a sequence as sort criteria. See line 24 of the stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0"
        xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
        xmlns:my="www.my-personal-namespa.ce"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">

<xsl:output indent="yes" method="xml"  />

<xsl:function name="my:sortierung" >
    <xsl:param name="inputstring" as="xs:string"/>
    <xsl:analyze-string select="$inputstring" regex="[0-9]+">
        <xsl:matching-substring>
            <xsl:value-of select="format-number(number(.), '00000')" />
        </xsl:matching-substring>
        <xsl:non-matching-substring>
            <xsl:value-of select="." />
        </xsl:non-matching-substring>
    </xsl:analyze-string>
</xsl:function>

<xsl:template match="/input">
    <result>
    <xsl:apply-templates select="value" >
        <xsl:sort select="string-join((my:sortierung(.)), ' ')" />
        </xsl:apply-templates>
    </result>
</xsl:template>

<xsl:template match="value">
    <xsl:copy-of select="." />
</xsl:template>
</xsl:stylesheet>

with this input:

<?xml version="1.0" encoding="UTF-8"?>
<input>
    <value>A 1 b 120</value>
    <value>A 1 b 1</value>
    <value>A 1 b 2</value>
    <value>A 1 b 1a</value> 
</input>

In my example, is there a way to modify the xsl:function to return a xs:string instead of a sequence?