You can try this (the code below comes from this site, of all sites..)
But if it doesn't work and it would take too much time to debug, I would suggest going for the pain of adding them manually once. Just put some good music and go for it... :)
@oefe I don't think VS.NET allows you to D&D projects into solutions, I've tried that once.
Imports EnvDTE
Imports EnvDTE80
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Private Shared Sub DoStuff()
Dim filePath As String = "c:\temp"
Dim fileName As String = "bld_TestApp.sln"
Dim fullName As String = Path.Combine(filePath, fileName)
Dim objType As Type
Dim objDTE As EnvDTE.DTE
objType = Type.GetTypeFromProgID("VisualStudio.DTE.8.0")
objDTE = DirectCast(System.Activator.CreateInstance(objType), EnvDTE.DTE)
Console.WriteLine(objDTE.Name + ":" + objDTE.Version)
objDTE.Solution.Create(filePath, fileName)
objDTE.Solution.AddFromFile("C:\Common.vbproj")
objDTE.Solution.SaveAs(fullName)
End Sub