.NET Custom Configuration object type based on attribute value

Question

I'm working on a custom configuration section for a custom application, attempting to make the functionality more easily extensible. I've got an extension mechanism finished up for one part, to create a specific configuration type based on the element name, but for another part I need to be able to do the same based on an attribute value, and I can't figure out how to access that before the ConfigurationElement object gets created and initialized from those values.

Basically, I have a set of FileFormat* objects which inherit from ConfigurationElement object, and I need to use the value of the 'type' attribute to instantiate the correct specific object (*DelimitedText, *FixedText, *Excel) so their type-specific properties can be initialized.

Here's the format of the ConfigurationElement's XML.

<format headerRows="1" footerRows="0" type="delimited" delimiter="|">
    <fields>
        <field name="fieldName" maxLength="50" required="true" />
        ...
    </fields>
</format >

Here's the code I'm trying to use to initialize it:

        private Lib.Core.Config.FileFormatBase _sourceFormat = null;
        [System.Configuration.ConfigurationProperty("sourceFormat", IsRequired = true)]
        public Lib.Core.Config.FileFormatBase SourceFormat
        {
            get
            {
                if(null == this._sourceFormat)
                {
                    System.String xml = this.SectionInformation.GetRawXml();
                    System.Configuration.PropertyInformation test = (System.Configuration.PropertyInformation)this.ElementInformation.Properties["sourceFormat"];
                    System.Configuration.ConfigurationElement element = (System.Configuration.ConfigurationElement)base["sourceFormat"];
                    System.String formatName = "";
                    this._sourceFormat = (Lib.Core.Config.FileFormatBase)Lib.Core.Config.FileFormatManager.Create(formatName, element);
                }
                return (this._sourceFormat);
            }
            private set
            {
                base["sourceFormat"] = value;
                this._sourceFormat = null;
            }
        }

        public static Lib.Core.Config.FileFormatBase Create(System.String formatName, System.Configuration.ConfigurationElement element)
        {
            System.Type formatType = GetRegisteredFormat(formatName);
            Lib.Core.Config.FileFormatBase handler = (Lib.Core.Config.FileFormatBase)System.Activator.CreateInstance(formatType, element);
            return (handler);
        }