MOSFET Cell Balancing Circuit
You could pull the gate up to the upper cell + terminal with the high value resistor and then pull it down to turn the MOSFET off, for example with a BJT or another MOSFET (open collector/open drain). 

However, the "threshold" voltage is not what you want to look at-- you want a gate voltage that will guarantee a certain Rds(on) so as not to cook your transistor. The only iron-clad guarantee on that datasheet is for 4.5V Vgs, so I would suggest using a MOSFET with guaranteed performance (Rds(on)) with 3V or lower Vgs. Also you should take care that the voltage under fault conditions (for example with the battery removed) cannot come close to exceeding the Vgs maximum rating (usually 10-20V, but sometimes lower). The MOSFET gate oxide can be protected with back-to-back zeners (between gate and source), if necessary.