As part of a recent project, I modified the DBDesigner 2 Propel XSL to convert MySQL Workbench *.mwb files to Propel schema. It has not been thoroughly tested, but this rough draft has been tested against my project using MySQL Workbench 1.1.4alpha on x86_64. If you have questions, please feel free to ask.

*UPDATE:

Kerry (hemisphere) fixed some issues with this and tried to post them in the comment below. Unfortunately, tags got stripped out, so I am posting his edits here:

There are two occurences of db.Column that should be db.mysql.Column and cause the foreign key references not to come out.

This 

<!-- ==== default ==== -->
<xsl:if test="value[@key='defaultValue'] != ''">
<xsl:attribute name="default">
<xsl:value-of select="@DefaultValue"/>
</xsl:attribute>
</xsl:if>

should be

<!-- ==== default ==== -->
<xsl:if test="value[@key='defaultValue'] != ''">
<xsl:attribute name="default">
<xsl:value-of select="value[@key='defaultValue']"/>
</xsl:attribute>
</xsl:if>

I added

<xsl:when test="$type = 'INT'" >INTEGER</xsl:when>
(from a MySQL db)
to
<!-- ============================================================
get_datatype -->
<xsl:template name="get_datatype">
<xsl:param name="type"/>

<xsl:choose>
<xsl:when test="$type = 'DATETIME'" >TIMESTAMP</xsl:when>
<xsl:when test="$type = 'TEXT'" >LONGVARCHAR</xsl:when>
<xsl:when test="$type = 'BOOL'" >BOOLEAN</xsl:when>
<xsl:when test="$type = 'ENUM'" >VARCHAR</xsl:when>
<xsl:when test="$type = 'YEAR'" >INTEGER</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$type"/>
</xsl:otherwise>
</xsl:choose>

</xsl:template>

VARCHAR size missing

<!-- ==== string length ==== -->
<xsl:if test="value[@key='length'] != ''">
<xsl:attribute name="size">
<xsl:value-of select="value[@key='length']"/>
</xsl:attribute>
</xsl:if>

The new version can be downloaded here: mysqlwb2propel.xsl