I run a123s too - same 5S1P pacs, usually run a pair wired in parallel so I have 4600mah for runtime. I charge mine at 10amps since thats all my Hyperions 0610i charger will allow. The newer 0720i will charge at 20amps so its getting better - charger designers are recognizing the need for more charger output power and higher charge rates.

Lipo uses the CC/CV charge routine - it charges at constant current (1C up to 5C as you mention) until the cells hit max voltage of 4.2v. The rest of the charge is at constant voltage allowing the cells to top off as amps decline.

I don't see any safe way for you to replicate this process with what you're using for a123s. You will damage a lipo overcharging - if not swelling it, then you're losing cycle life due to internal changes you're causing.

Get one of the high power chargers that will charge at high rates and protect yourself from destroying or compromising an expensive lipo. Oh the other thing - do some more research - the significant time savings comes from jumping from 1C to 2C charging with lipo due to the way the CC/CV routine works.