I've done this on drone 4S lipos, it does work.
Connect lipo to charger, put it lipo blanket or ammo can for safety. Set charger to NiMh charge at lipo MAH. Set amps to .50amps(half amp). You dont want to force it, Every 15sec Start and Stop, and 15sec rest. #4 cell will incrrease. When it reaches 3.8V stop there. Be patient It take time! maybe 15-30min.
When reaches 3.8V, change charger to Balance Mode, set amp to MAH rated at, 4S Start Charger It should start charging. Check LI Batt Meter on charger and monitor Balancing charge And check temp on battery pack.
Respone to post if need questions.