I do not know about an easy way to use. I considered using dom4j (because I use it for other purposes, but any other universal xml manipulation library is equivalent) and manually create it (1).
But then I realized that I could use JAXB to create an xml schema object model, populate it with what I wanted (it turned out to be much less convenient than I had hoped for) and marshall it (2). Its through JAXB, but without creating classes for your schema, so maybe this could be useful for you.
after 2 it is difficult (but not impossible) to create an invalid circuit, but sometimes it is difficult to determine how to create the circuit that I wanted. So I finished creating it in the editor, then parsed it and examined its representation of the object. In the end, creating it through 1) and then confirming it (which I should have done anyway) would be less time consuming.