Use the following trick to kill Alien Troopers without shooting. When the 
Alien Troopers jump in the air and levitate shortly doing nothing, they are 
about to charge at you, which may kill you in one hit. When they do this, 
get out of the way. When they charge and miss, there will be a moment where 
they are idle. Run up to them, grab, and throw them. This may be slightly 
difficult at certain angles. The moment you throw them they will die (under 
the Easy difficulty setting at least).