Replace desktop computers with laptop computers.
These can be locked ont othe office desks for safety and removed by those who are permitted to use them away from the desk.
According to Natural Resources Defense Council,
"conventional desktop computer with a conventional cathode ray tube (CRT) monitor uses more than five times as much energy as a laptop (570 kWh/yr vs. 100 kWh/yr ).
Therefore, replacing a desktop system with a laptop system could save a user over 450 kWh/yr – nearly $40 annually".
Ref: Laptop Computers: How Much Energy Do They Use and How Much Can We Save?