Upload & Sell: Off
Easy to do with one accessory HS.
Instead of plugging your PW into the PC link socket link on your EXII. Plug you PW into an acc' HS. (if you're using an EXII, if not, then you will be using an accessory HS anyway).
Set the PW triggered 580 as your main, set your other 580 as slave. Mode on M, set your power levels and it all works.
PW into acc' HS ...
Another view ...
Set this PW'd 580 as your main flash as you would using the Canon system ...
The master flash is being illuminated with a Slaved 580 which is picking up the usual Canon IR signal ...
If you use TTL/ETTL you are going to have a FULL power flash as there are no camera readings for the TTL to work out.
When I had only two PW, I use to fire 3 580s and a 550 this way. Works fine with all the usual line of sight considerations.