Critter,
yes there are cut outs available to wire in line for lipos.
Or you can use the timing method. time flights, landing occasionally to check pack volts. Once you reach limit for pack. deduct a couple of min from limit, for just in case factors.
Note: A 2 cell lipo will actually perform better and longer then stock packs. Even though it is lower voltage then say an 8 cell, it will hold same volts for a longer time. Regular packs start out high and drop drastically on the volt side.