Ok, forget the idea. I'd forgot that the amps don't add up, so nothing to gain even if it did work, and it probably won't work anyway.
That's the way I'm doing it now, 3 separate chargers on the 3 12v batts that make the 36 volts, but its a pain to get at all the batteries.
I just got a new 36v charger, but it turned out to be 1.5 amp, instead of the 3.1 amps as advertised. And for $11.89, I'll make it work I guess, being as I have more time than money :)