You can't do this with any native methods in the Outlook Object Model, but
you can using Outlook Redemption (http://www.dimastr.com). If you copy the
selection in Excel and have an open e-mail, run this function:
Sub PasteClipboardContentsIntoBodyActiveItem()
Dim sInspector As Object, objPlainTextEditor As Object
Set sInspector = CreateObject("Redemption.SafeInspector")
sInspector.Item = Application.ActiveInspector
Set objPlainTextEditor = sInspector.PlainTextEditor
objPlainTextEditor.PasteFromClipboard
Set sInspector = Nothing
Set objPlainTextEditor = Nothing
End Sub