Gaining permanent control of a Chryssalid/Tentaculat

In order to gain permanent mind control/molecular control over a Chryssalid or Tentaculat, mind control/molecular control a zombie and shoot it. The tentaculat/chrysallid that will appear is hostile, but don't kill it. Next turns it will be controlled by you for the rest of the mission. if you used a soldier/aquanaut he will be back after the mission.