Last time I checked there wasn't a built in configuration builder similar to what you could find in PageTypeBuilder.

If you have an existing PropertySetting or creating one at startup I guess you can use an EditorDescriptor to set your configuration.

Checkout EPiServer.Cms.Shell.UI.ObjectEditing.EditorDescriptors.XhtmlStringEditorDescriptor in the EPiServer.Cms.Shell.UI (usually found in the Modules-path among your VPP) for some inspiration.

    public override void ModifyMetadata(ExtendedMetadata metadata, IEnumerable<Attribute> attributes)
    {
      base.ModifyMetadata(metadata, attributes);
      TinyMCESettings settings = (TinyMCESettings) ((PropertyData) metadata.Model).GetSetting(typeof (TinyMCESettings));
      ExtendedMetadata mostContentMetadata = ExtendedMetadataExtensions.FindTopMostContentMetadata(metadata);
      IContent content = mostContentMetadata != null ? mostContentMetadata.Model as IContent : (IContent) null;
      TinyMCEInitOptions tinyMceInitOptions = new TinyMCEInitOptions(TinyMCEInitOptions.InitType.EditMode, settings, content);
      if (metadata.IsReadOnly)
      {
        tinyMceInitOptions.InitOptions["readonly"] = (object) true;
        tinyMceInitOptions.InitOptions["body_class"] = (object) "mceReadOnly";
      }
      metadata.EditorConfiguration.Add("width", tinyMceInitOptions.InitOptions["width"]);
      metadata.EditorConfiguration.Add("height", tinyMceInitOptions.InitOptions["height"]);
      metadata.EditorConfiguration.Add("settings", (object) tinyMceInitOptions.InitOptions);
    }