Is it possible to set an env value in a task from a variable passed in when call the task?

I would like to call a task like

task start-service use_mocks=true

task start-service use_mocks=true

And have that set a env value in my start-service task like

start-service:
  vars: 
    use_mocks: false
  env: 
    user_mocks: {{.use_mocks}}

start-service:
  vars: 
    use_mocks: false
  env: 
    user_mocks: {{.use_mocks}}

That exact setup doesn't but I'm wondering if there is another way to do it? I want a default value of false and if passed it uses the passed in var