When using the SaveAs method you get the default behavior and don't have control over the various translator settings. In order to control the setting you need to drive the translator directly. There are several samples in the API help that demonstrate this and there's on in particular that shows how to write out a STEP file. The sample doesn't show all of the options that are available. That's also listed in the API help but when I just looked for it now found it's not accessible through the index. Instead you have to search for it. We need to correct this. In the meantime, I copied and pasted the material in a Word document, which I've attached. You'll see the option for excluding sketches there.
Brian Ekins Developer Technical Services Autodesk Developer Network Autodesk, Inc.