Why not attend by telepresence? Let him present by video and hook him up with a Double or similar internet-controllable robot to talk to people around the conference. Or go full-on Bluth and pair up with an American proxy wearing a headset.
I've been thinking you could hook up a cam/mic to one of those Roomba vacuum 'bots and then you could cruise around the conference and network with your colleagues just as though you were there. I understand those things have wifi already, so....
The coolest part would be bumping into other Roombas that represent colleagues from elsewhere (you'd need a way to distinguish from an ordinary, autonomous Roomba). There could even be a Roomba room just for them!
Someone did this a while back -- it made HN, but I don't remember who was behind it. It had a camera and an LCD display and could travel between offices and conference rooms in an office building several states away, attending meetings and generally hanging out with coworkers.
If this would become common (or any "other way"), it could very well be made illegal shortly after and requires some sort of visa. The issue is not technical, it's political.
This sucks, sure, but there's always another way.