How to configure OWIN Web API 1 via IAppBuilder - owin

Question

TL;DR: How do I configure OWIN Web API 1 via a StartUp class or alternatively use the HttpSelfHostServer with the static files extension?
I have a working self-hosted OWIN Web API 2 project, which I'd like to downgrade to .Net 4.0 - I'd prefer not to install the .Net 4.5+ framework replacement, because of unknown side-effects on a production machine.
I can't use Microsoft.AspNet.WebApi.OwinSelfHost because it's not available for .Net 4.0 and therefore I can't call the IAppBuilder.useWebApi() extension method for registering my configuration.
I'm bootstraping the server now like this: WebApp.Start(Of StartUp)(url:="...")
and the StartUp class looks like this, but I can't set the config:
Public Class StartUp
Public Sub Configuration(app As IAppBuilder)
' the host should be obsolete, as it's already configured in the app context
Dim config As New HttpSelfHostConfiguration("http://localhost:9000")
' config.MapHttpAttributeRoutes()
config.Routes.MapHttpRoute(
name:="DefaultApi",
routeTemplate:="api/{controller}/{id}",
defaults:=New With {.id = RouteParameter.Optional}
)
' configure formatters, converters, filters ...
' app.UseWebApi(config)
Dim physicalFileSystem As New PhysicalFileSystem("...\static")
app.UseDefaultFiles(New DefaultFilesOptions With {.FileSystem = physicalFileSystem})
app.UseStaticFiles(New StaticFileOptions With {.FileSystem = physicalFileSystem, .ServeUnknownFileTypes = True})
End Sub
End Class
If I'd use the documented Web API 1 approach of bootstrapping the server (see below), I don't know how to configure the static files extension:
var config = new HttpSelfHostConfiguration("http://localhost:8080");
config.Routes.MapHttpRoute(
"API Default", "api/{controller}/{id}",
new { id = RouteParameter.Optional });
using (HttpSelfHostServer server = new HttpSelfHostServer(config)) {
server.OpenAsync().Wait();
Console.WriteLine("Press Enter to quit.");
Console.ReadLine();
}
Although I've checked the AspNetWebStack sources, I think the message handling has changed between V2.1.0 and V5.0.0+ and therefore I can't apply that approach.
I'm using the following nuget packages - which I might reduce after its working:
<packages>
<package id="Microsoft.AspNet.WebApi.Client" version="4.0.20710.0" targetFramework="net40" />
<package id="Microsoft.AspNet.WebApi.Core" version="4.0.20710.0" targetFramework="net40" />
<package id="Microsoft.AspNet.WebApi.SelfHost" version="4.0.30506.0" targetFramework="net40" />
<package id="Microsoft.Net.Http" version="2.0.20710.0" targetFramework="net40" />
<package id="Microsoft.Owin" version="2.1.0" targetFramework="net40" />
<package id="Microsoft.Owin.Diagnostics" version="2.1.0" targetFramework="net40" />
<package id="Microsoft.Owin.FileSystems" version="2.1.0" targetFramework="net40" />
<package id="Microsoft.Owin.Host.HttpListener" version="2.1.0" targetFramework="net40" />
<package id="Microsoft.Owin.Host.SystemWeb" version="2.1.0" targetFramework="net40" />
<package id="Microsoft.Owin.Hosting" version="2.1.0" targetFramework="net40" />
<package id="Microsoft.Owin.SelfHost" version="2.1.0" targetFramework="net40" />
<package id="Microsoft.Owin.StaticFiles" version="2.1.0" targetFramework="net40" />
<package id="Microsoft.Web.Infrastructure" version="1.0.0.0" targetFramework="net40" />
<package id="Newtonsoft.Json" version="4.5.6" targetFramework="net40" />
<package id="Owin" version="1.0" targetFramework="net40" />
</packages>
Btw. although I've used VB.Net in the example, feel free to use your preferred language in your answer.