If you're looking solely for direct flights, you seem to have most of the options already.
The Manchester Airport website lists the only direct flight operators as American Airlines, BMI, Finnair and PIA. However, the Finnair website does not refer to the route (which suggests that the service, which might have only been a code-share arrangement with one of the other operators anyway, has been discontinued). I couldn't find any relevant information on the PIA site but their fares are usually very high. You state that you've already tried BMI and I've suggested American Airlines. That would seem to cover all of the options.
For some sample dates, just after Easter, American Airlines quote �647.20 for direct flights. They also offer �603.70 via JFK but, if you could persuade your friend to change flights, it would be much cheaper to travel with Delta, via Newark.
Otherwise, for direct flights, the only option would appear to be to travel to another UK airport.
Chris