If no luck with SPservices, take a look at qRules from Qdabra. It allows you to inject code using rules into Infopath forms, and one of its functions is to detach attachments into a library and replace the attachment with a link in the InfoPath form.
http://www.qdabra.com/en/products/qRules_new.aspx
http://www.qdabra.com/en/products/qRules_new.aspx