RAM upgrade on PowerEdge TT710

I want to do a RAM upgrade on a PE T710. Currently I have 24 GB of RAM installed in optimizer mode,

there are 18 sockets total, 12 sockets x 2 GB of RAM,sockets A1 through A6 and B1 through B6 are populated,  2 physical chips in the motherboard.

I'd like to just add 4 sticks of 8GB of RAM and bring it up to a total of 56 GB of RAM but my problem is that the

documentation says that even though I can mix memory modules of different sizes, the configuration for all

channels has to be identical. Does this mean that I can't just add 8GB of RAM to sockets A7, A8, B7 and B8 ?

thanks

John