You can use this step-up/step-down voltage regulator to output fixed 3.3 V through its whole discharge cycle of your battery.http://www.pololu.com/product/2122
and it will cut off at 2.7V
My mistake on assumption that the regulator will cut off below 2.7V
will NOT protect a LiPo from overdischarging and that a separate protection circuit is therefore required.
It does not enter shutdown mode until the input drops to around 1.8 to 2.2V, it is possible to continue draining your battery when the voltage drops below 2.7V.