Wouldn't it be easier / quicker to balance charge them together in pairs as 4s with one of these cables:
http://www.rctechnics.eu/splitter-ad...ml?language=en
I guess you would need to charge them separately first time then once you've used them in series as 4s once then you should be ok to charge as above?
I'm not sure about all this, but that's what I was planning to do, please let me know if I'm about to set fire to my garage!