Here's the navigation view code I have currently...

@using EPiServer.Core
@using EPiServer
@using EPiServer.Filters
@using epiSalesDemo.Helpers
@using EPiServer.Web.Mvc.Html
@using EPiServer.ServiceLocation
@using EPiServer.SpecializedProperties
@using EPiServer.Web.Routing
@using epiSalesDemo.Models.Pages

@{
    var contentLoader = ServiceLocator.Current.GetInstance<IContentLoader>();
    var mainNavRef = contentLoader.GetChildren<PageData>(ContentReference.StartPage);
    var home = contentLoader.Get<HomePage>(ContentReference.StartPage);

    PageData sp = DataFactory.Instance.GetPage(PageReference.StartPage);

    bool showSecondLevelNavigation = true;
    bool showThirdLevelNavigation = false;

    PageRouteHelper pageRouteHelper = EPiServer.ServiceLocation.ServiceLocator.Current.GetInstance<PageRouteHelper>();
    PageData currentPage = pageRouteHelper.Page;
    PageData parentPage = DataFactory.Instance.GetPage(currentPage.ParentLink);
    
}

<nav>
   <ul class="clearfix main-nav">
   @{
      IEnumerable<IContent> SubNav = new PageDataCollection();
      IEnumerable<IContent> ThirdNav = new PageDataCollection();

      foreach (PageData topLevelPage in mainNavRef)
      {
         if (topLevelPage.HasTemplate() && topLevelPage.VisibleInMenu && topLevelPage.IsVisibleOnSite())
         {
            bool IsCurrentPage = false;
            if (topLevelPage.ContentGuid == parentPage.ContentGuid) { IsCurrentPage = true; }
            IsCurrentPage = currentPage.PageGuid == topLevelPage.PageGuid || IsCurrentPage;

            @:<li class="@(IsCurrentPage ? "highlight" : "")">@Html.PageLink(topLevelPage)

            SubNav = contentLoader.GetChildren<PageData>(topLevelPage.ContentLink);
            bool weHaveSubPages = false;
            foreach (PageData subPage in SubNav)
            {
               if (subPage.HasTemplate() && subPage.VisibleInMenu && subPage.IsVisibleOnSite())
               {
               weHaveSubPages = true;
               }
            }
            if (weHaveSubPages && showSecondLevelNavigation)
            {
               @:<div class="nav-sub clearfix"><div class="large-6 column"><ul>
                   foreach (PageData subPage in SubNav)
                   {
                      if (subPage.HasTemplate() && subPage.VisibleInMenu && subPage.IsVisibleOnSite())
                      {
                         @:<li>@Html.PageLink(subPage)</li>
                      }
                   }
               @:</ul></div>

               @:<div class="large-6 show-for-large-up column">
                      DISPLAY CUSTOM CONTENT FROM MAIN NAV PAGE HERE
               @:</div></div>
            }
            @:</li>
         }
      }
   }
   </ul>
</nav>

I think you could have your custom block that contains a ContentReference and other custom content you might have. Then your main navigation is list of your custom blocks