What do you mean by "may have been over-discharged." IMO, you don't have any business using lipos if you don't have even a relatively inexpensive multimeter for measuring the voltage of each cell via the 4-pin balancing charge connector.

The first thing you need to do is check the voltage of each cell. Then depending on their condition you might be able to restore life to the LiPo by slowly charging it at 0.2C. So, for example if its rated at 1000mAh you would set your charger to 0.2 amps and measure each cells voltage every 15 minutes the first hour and then every hour keeping tabs on any noticeable temperature or cell puffing until the LiPo hopefully reaches 12.4v-12.5v, then STOP!

FIRST CHECK EACH CELL'S VOLTAGE WITH A VOLT METER. If the voltage of even just one cell is below 2.7v you are best adviced to discard the LiPo. If you don't get any voltage reading you may want to first hook it up to the charger at 0.2 amps for 1-2 minutes and then check each cell again to see if they fell asleep and if they are all now above 2.7v.

THERE IS NO REASON WHY YOU CAN'T CHARGE A LIPO VIA THE DISCHARGE CONNECTOR IF ALL THREE CELLS ARE OF EQUAL VOLTAGE/QUALITY.