Disposing members of an instance of an unknown type

[Warwizard]

This is for a program that has a built-in script system (using CodeDom), and requires the objects that were created by the script to be disposed before updating/re-compiling the script, in order to stop the execution of the older assembly.

I'm trying to make a generic method to dispose an instance of any class, so that scripters don't need to implement IDisposable.

Let's say the scripter created a class, with unknown contents, that may not implement IDisposable.
Like this:

Public Class foo
    Dim obj1 As New managedType1()
    Dim obj2 As New managedType2()
    Dim var1 As unmanagedType1
End Class

Dim myFoo As New foo

How to dispose myFoo?

I've tried it this way (with a class that has StructLayout attribute):

Public Shared Sub DisposeObj(ByVal obj As Object)
        If TypeOf obj Is IDisposable Then
            CType(obj, IDisposable).Dispose()
            Exit Sub
        End If
 
        Dim typeOfObj As Type = obj.GetType()
        If typeOfObj.StructLayoutAttribute Is Nothing Then Exit Sub
 
        Dim gch As GCHandle = GCHandle.Alloc(obj)
        Dim offset As Integer
        Dim memberObj As Object
 
        'try to dispose the members of this class
        For Each member As Reflection.MemberInfo In typeOfObj.GetMembers(Reflection.BindingFlags.NonPublic Or Reflection.BindingFlags.Instance Or Reflection.BindingFlags.DeclaredOnly)
            offset = Marshal.OffsetOf(typeOfObj, member.Name).ToInt32
            memberObj = GCHandle.FromIntPtr(New IntPtr(GCHandle.ToIntPtr(gch).ToInt32 + offset)).Target
 
            DisposeObj(memberObj)
        Next
    End Sub

But line 17 returns obj. I know this wasn't even supposed to work, because the offset doesn't tell where the member instance is allocated.

Any other ideas?