OK, so here's something I posted a while back on rec.juggling for Rusty:
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I'm not sure there is an "easy" way to start 3 diabolos!

You have the
option of starting with 1, 2, or 3 diabolos on the string. 1 or 2 would be
far easier unless you've already mastered 3 diabolos low (that certainly
is NOT easy!). Most people start with one on the string and throw two
others but you could start with 2 on the string with one in a right stick
stopover and both sticks being held by your left hand. You'll have to
angle the stick in a way to keep the string from slipping. (If all else
fails, double sided tape will keep it from slipping.) Then throw one
diabolo up and launch the bottom diabolo followed by the stopovered
diabolo in a smooth motion.
In terms of throwing technique. I don't think there is a throwing
technique not mastered by someone. So pretty much, whatever works for you
works! The options are: (assuming right handed diaboloing)
-Backhanded spinning of the diabolo with the left hand facing the right or
backhanded spinning of the diabolo with the right hand facing the right.
In these cases you could throw in an arc back over your head opposite to
the arc that the pattern will take (like Tony (left hand) with 4 diabolos
or Priam (right hand)) or forward into the correct arc (like Ryo Yabe).
You put your middle finger around the axle, spread your fingers out and
use bit of wrist and arm motion to spin the diabolo.
-Underhand, right handed flat hand spinning, facing to the left. Your hand
is flat (no finger around the axle) and facing to the left. This method
starts the diabolos in the right arc (good) and gets more spin generally
(good) but seem a bit awkward for some people (myself included). 3 people
I know of that have fully mastered this: Jibe, Tony (with 3 diabolos), and
Fred (also from France). Tony uses this for 3 diabolos I've been told
because it creates more spin but it isn't fast enough for him to do 4 or
more diabolos - so he switches.
In general, whatever way you decide to use will take many months to become
at all reliable. Assuming you already have 2 diabolos high mastered and
some 2 diabolo high tricks 3 diabolos high should take a bare minimum of 2
to 3 months of daily practice before you experience any success with it
and many many more before it's solid. Practice lots with throwing up the 2
diabolos by hand and starting from there (if that's how you decide to
start the patten). It's not easy... but that's what makes it so worthwhile!
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Hope that helps a bit and gets a discussion started.
Sean