is your dual charge lead setup parallel style? if those boards dont work, you could always buy/make up a parallel set of balance plugs as well.

but what is your reason to do this? can your charger put out enough that it will charge 2 at a time faster than one out of a time. my charger only does 5 amps, and my batteries can be charged at 5 amps... so if I put two batts on at a time Im not charging any faster. and you cant say that way I can walk away and have hours without having to swap batteries on the charger, because you cant(not supposed to) leave them unattended.