graphical mapper: existence of optional nodes

BizTalk 2009

Hi.

I have a flat file with fixed field lengths and optional segments, like these 3 messages:

HEAabcPATdef
HEAabcANGdef
HEAabcPATdefANGghi

The start of each message is marked by HEA and the end by CrLf.
In my example each message can have 3 segments starting with HEA, PAT and ANG. Each segment has 2 elements. The cardinality of the HEA segment is 1 and of the others 0 or 1.

The first message of the example should be transferred to such XML

<SapBatch>
<Sap>
  <HEA>
    <SegName>HEA</SegName>
    <ElmHea>abc</ElmHea>
  </HEA>
  <PAT>
    <SegName>PAT</SegName>
    <ElmPat>def</ElmPat>
  </PAT>
</Sap>
</SapBatch>

Although I specified Min and Max Occurs in the schema, I learned from the web to put a Sequence node in front of the optional segments like this:

It works fine.

Now I use this schema as source in a mapping. Because of the Sequence nodes, the mapper puts around the optional segments such code:

<xsl:for-each select="Sap/PAT"> ... </xsl:for-each>

I want to check in the graphical mapper the existence of the PAT node. I cannot put functioids to that node, because the code within <xsl:for-each select="Sap/PAT"> is ignored if PAT is missing.

Then I used the XSL code of the mapper and put around <xsl:for-each select="Sap/PAT"> this code for the check:
      <xsl:choose>
        <xsl:when test="not(SapHcm/PAT)">
          ...
        </xsl:when>
        <xsl:otherwise>
          <xsl:for-each select="SapHcm/PAT">
  ...

I assigned the so modified XSL code as file to the map and it does what I want. But I don't have the graphical view of the mapper anymore and this is very helpful because my schema is much bigger than showed here.

So my question: How can I check in the graphical mapper the existence of optional nodes?

I would be happy for every hint