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Yes, that could work. You'd need a choke in series with the fet to limit the rate of rise of current - you'd effectively be making a switch-mode power supply! Also, a temperature sensor on the fet. Is that simpler than a current sensor? And why use a fet? A bipolar transistor might be better as its easier to drive from a logic level.
So there you go: A pwm drive output from the micro, a bipolar power transistor, a choke and a small resistor in the emitter lead of the transistor to act as a current sensor feeding into a spare adc input on the micro. The transistor is turned on and the current monitored - transistor turned off when I reaches the desired level. Oh, you'd need a Schottky diode across it as well to absorb the voltage spike when the transistor turns off.
All this to shift the heat dissipation from a resistor to a transistor.
If anyone can think of a clever way of sending this power to the cell with the lowest voltage, you might have something.
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