Hi ActiveT and welcome to our forum!
Does the form have a main data source derived from the Web service or is it separate from the Web service (I'm guessing the latter, but need to know). There are some tricks using eval function to concatenate strings and my guess is that you may be able to do a similar thing where you have a rule that fires at the parent and sets a counter that you use to index the child in the secondary data source and copy the resutls to the main data source. Shouldn't be too hard to implement using rules and xpath. Of course, you could just do it in code too.
Patrick Halstead
Project Manager at Qdabra