This is a quick video that shows how a SharePoint SmartObject can be used to upload InfoPath attachments to SharePoint rather than store the attachments in the InfoPath form itself.
You can also have a look at Johnny's blog and the .pdf he uploaded to see a more detailed account how this is accomplished.
www.k2underground.com/.../the-proper-way-to-attach-files-in-k2-infopath-processes.aspx