that's not how it's done, but can be used sometimes.
real bias networks in IC's kill the gate voltage to shut off the bias network.
for a set of pmos mirrors, you'd add a pmos between vdd and the gate connections. now when you turn this pmos on, it pulls the gates of all your mirrors to vdd and shuts off your bias currents.
a similar trick for nmos mirrors, except now the shutdown transistor is nmos, and pulls the gates of your nmos mirrors to ground, shutting off the nmos currents.
hope this helps!