Using Configurator items from any external system is a very difficult task. I've never seen anyone successfully roll their own solution for that problem, which I've tried to do before.
I have seen a CDI product called "ERP2Web" successfully integrate with Configurator. They have a nice web interface to allow customer self-service for ordering configured items. I took a cursory glance at how they solved that problem, but it included some of their own custom BSFNs developed within OMW to make it work.
They also have a function that lets your customers (or CSRs) submit Excel spreadsheet uploads that contain Configured segments, and could probably expose that functionality to you as a webservice.
Beware: Configurator segments are ugly and very difficult - if not completely impractical - to use as a webservice. The spreadsheet method I've seen in ERP2Web is ugly for Configured items because of the complicated nature of Configurator segments. But, it can be done if you are truly willing to trudge through it.
IMO, Configurator is much more practical to use interactively. If you really want to automate via webservice, try to consolidate some of your most-used Configurator items into stock BOMs and develop an alternative business process for when Configurator is truly required.
My $0.02 on the matter.