I would just look at a new charger like the maha c9000 which i got for my tk40. I was going to do a 4aa series holder but you can't charge the batteries above much more then amp other wise you risk melting the holder.
The Maha C9000 will only charge 4 batteries at a time. This light holds 8 batteries.
The advantage of buying a smart charger like one of these..
http://www.batteryspace.com/smartchargersfornimhcdbatterypackseries.aspx
Is that they are designed to charge packs in a range ov voltages/cells which they automaticly detect.
Your assumption that charging a larger pack would have to be done at a higher current is incorrect. I have a CHUN-180. It will detect the voltage to apply and the higher the pack the more voltage, but it will limit the current to a charging current that you select.
http://www.batteryspace.com/multi-c...6v-18vnimhbatterypackstamiyaplugullisted.aspx
which I use for a variety of lights and other devices, in fact all my NIMH needs (including TK40 and Mag85)and I charge at .9 Amps. I use the radio shack 8 cell holder so I can charge them all at once and insure they are balanced. The CHUN smart charger just clips right on, and in the case of my FIVEMEGA battery holder for my Mag85 it plugs right in (thanks Fivemega).
It's quicker and easier, although if you don't mind doing 2 complete charging sessions with your Maha C9000, which only holds 4 cells, it should work, but if your willing to put out almost $50 for that charger I don't know why you wouldn't just get one that will do the job all at once.
You really don't want to charge enelopes at more than an amp. anyway, unless you want to substitute safety, longevity and a complete charge, for speed. And if this is the case, then why buy a charger that can't charge your whole pack at once?
There is no chance of melting the holder at NiMH charging amperages.
Anyhow to each their own, I'm just recommending a solution that I've been using for 6 months with 0 problems. I sure wouldn't want to pay 50 bucks to double my charge times by only charging a half of a pack at a time.