BizTalk mapper: XSD CHOICE group; suppress child node with attribute with default value

Hi guys

 we have an urgent issue that we are trying to resolve prior to demo-ing to a client next week the benefits of using BTS(!)

 We have a legacy XSD that has a number of cases where there is a CHOICE group that contains a number of child nodes: only 1 of these child nodes should appear in the output message. However, most of these children (or their descendants somewhere down the line) have optional attributes that default values, the intention being that if (and only if) you create an instance of that child then a default value can be supplied for this attribute.

In the BTS mapper we map the fields from the input message to the single choice/child node that we need: however, behind the scenes the BTS mapper is also creating an instance of each of the children in the choice group that has an attribute with a default value; we see this in the xsl when we validate the map, and we can see all these extra nodes if we switch off output validation when we test the map; if we leave output map validation on then the output fails the validation because we have broken the choice rule (i.e. more than one of the choices is in the output message).

I know that we could get rid of all the default values in the xsd but (a) the xsd is not owned by us and (b) it seems perfectly legitimate to have these defaults in there.

So the question is: how do we stop the BTS mapper auto-generating unwanted instances of CHOICE group child nodes that have attributes with default values??

Many thanks in advance

Bob