Hi guys,
It has been done before with inflatables also and pretty much set up like Kiteboy Dave mentioned except I think the distance between the two kites was more like 5 metres which reduces the amount of "V" of the lines between the kites and I think a little less than 8-12 cm in rear line length difference.
It is good to think out loud and the thought is interesting but ....
Wakeboarding is more fun in 6 knots .... at least then you can jump!
It's all fun and games until they luff

and fall from the sky

You thought swimming one kite in was a hassle. [}:)]
We also thought about towing a guy on a kite behind a boat ... ask me about this if you see me at the beach and I'll tell you how that ended up.

Good winds and Peace