Does there exist, software or technology, that can use more than one wifi network, in such a way that only part of the data travels through each 'side'? You would probably need an end address like a proxy. Something similar to TOR, except each primary network wouldn't be able to intercept all the data sent or received.
Bonding two channels to the same AP is done. But you want to take it one big step further.
You could perhaps do something of the kind using two wireless cards, two separate ESSIDs and some fancy footwork at kernel level (not all OSes would be able to do that), using bonding; or, even more complicated, by using two WiFi chips on a card that would simulate a single interface and do bonding transparently (you would need special access points though - you'd be in effect doing SuperG using two APs on the same network).
But it would be very difficult to overcome all the problems - and it would be all for naught, because the radio signal would be traveling in the same volume of space, where an attacker could sniff both signals. True, he would have to decrypt two conversations instead of one, but that's a mere 2^1 increase in the hardness of the attack. Employing additional encryption over the existing WPA2 would be far easier, and garner a lot more benefits for much less effort.