Part of the OWE rules states that two entries/exits from Europe are allowed if one of them is a transit (via LHR) to/from Ghana/Nigeria. I had an AONE6 and I was trying to maximize mileage and status credits. I remember reading about someone (tfung?) who had also done an Accra transit some time ago, but hadn't heard of anyone doing one recently. There weren't any problems this time around so I assume things have improved considerably since the 70's!