Seeing this has remained unanswered for quite a while, I will offer my incomplete reply. I once flew this way but it was many years ago - the company was called something like Pony Express and had a tie-up with BA with a base near Heathrow. They may no longer exist as such. However, the only way I can suggest for line of enquiry is to contact the likes of DHL, Federal Express and UPS. The system is that you can agree to fly one or both ways through them, you must agree to take their material with you as baggage (often only hand baggage, occasionally nothing) but your allowance remains the standard. You choose the date(s) you want to fly and usually pay some standard fare which need not be hugely different from the cheapest available through conventional sources, but sometimes it is a lot cheaper. The choice of Destinations is not enormous (may be quite limited). Somebody was clearly doing this for FedEx on a flight I was on recently, but she could have been a member of their staff (as sometimes is the case).