John,

Hit a road block with your suggestion.  Created a skin called subportal.ascx and can't get past:
this error: I Tried various combination and mods etc.  Is your code specific to any particular DNN codebase?

ExceptionGUID: 713b84a0-feb3-44a1-9847-faf02a41e29f
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
InnerException: Unhandled error loading page.
Message: DotNetNuke.Services.Exceptions.PageLoadException: Unhandled error loading page. ---> System.Web.HttpException: External component has thrown an exception. ---> System.Web.HttpCompileException: External component has thrown an exception. at System.Web.Compilation.BaseCompiler.ThrowIfCompilerErrors(CompilerResults results, CodeDomProvider codeProvider, CodeCompileUnit sourceData, String sourceFile, String sourceString) at System.Web.Compilation.BaseCompiler.GetCompiledType() at System.Web.UI.UserControlParser.CompileIntoType() at System.Web.UI.TemplateParser.GetParserCacheItemThroughCompilation() --- End of inner exception stack trace --- at System.Web.UI.TemplateParser.GetParserCacheItemInternal(Boolean fCreateIfNotFound) at System.Web.UI.TemplateParser.GetParserCacheItemWithNewConfigPath() at System.Web.UI.TemplateParser.GetParserCacheItem() at System.Web.UI.TemplateControlParser.CompileAndGetParserCacheItem(String virtualPath, String inputFile, HttpContext context) at System.Web.UI.TemplateControlParser.GetCompiledType(String virtualPath, String inputFile, HttpContext context) at System.Web.UI.UserControlParser.GetCompiledUserControlType(String virtualPath, String inputFile, HttpContext context) at System.Web.UI.TemplateControl.LoadControl(String virtualPath) at DotNetNuke.Framework.CDefault.LoadSkin(String SkinPath) --- End of inner exception stack trace ---

Wow... 2 hours of hair pullin on this one....  I modified your code for testing as long as your not logged in as admin or host ;( 

< %@ Control language="vb" AutoEventWireup="false" Explicit="True" %>
< asp:placeholder id="SkinPlaceholder" runat="server" />
< s c ript runat="server">
        Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim skin As String = ""
        skin = "fixed-width.ascx"
        SkinPlaceholder.Controls.Add(LoadControl(skin))
    End Sub
</ s c ript>

Works fine and a modified rev passing the subportal info works too.  BUT when your logged in as admin  or host you can't get to the page. :

An error has occurred.
DotNetNuke.Services.Exceptions.PageLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.UI.Skins.Skin.Page_Init(Object sender, EventArgs e) at System.Web.UI.Control.OnInit(EventArgs e) at System.Web.UI.UserControl.OnInit(EventArgs e) at System.Web.UI.Control.InitRecursive(Control namingContainer) at System.Web.UI.Control.AddedControl(Control control, Int32 index) at System.Web.UI.ControlCollection.Add(Control child) at ASP.subportal_ascx.Page_Load(Object sender, EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain() --- End of inner exception stack trace ---

Which kind of makes managing content difficult...  Hmm...  Time for a Scotch.  John.. I'm buyin...