Shutdown for LT3080 current source
Depending on your load you may be able to just force the
SET pin to GND. 

If you pull the SET pin to GND the LT3080 
will force the OUT pin to 0V. The internal schematic shows 
that the SET pin connects to the positive input of the control 
amplifier and the OUT pin connects to the control amplifier 
output (through a transistor buffer). The OUT
pin follows the voltage on the SET pin. 

Use an N channel FET to short the SET pin to ground.