How to use a (cheap) BMS for discharge only
The simplest workaround to an un-activated BMS (sleep mode) is to supply it with power from it's own batteries. To achieve this, a push switch/momentary switch can be used between the P- and B- terminals of the BMS. 



Note: This will work only if the cells have adequate voltage. The BMS will return to sleep mode if the individual voltages are too high or too low.