ec2 multiple security groups using a variable

[Joe]

We've recently had to add multiple security groups to an ec2 instance, but based on the host group, it needs to be a different set of groups.
I see that you can do this by using an array list like so:

  - name: launch

      local_action:

        module: ec2

        region: us-west-2

        keypair: xxxxx

        group: ['mygroup1', 'mygroup2', 'mygroup3']

        instance_type: t1.micro 

        image: ami-xxxxxx

        wait: yes

        wait_timeout: 3500

        count: 2

        instance_tags: '{"Name":"stuff"}'

      register: ec2

This will work fine when hard coded, but when i replace the list with a variable it does seem to detect the groups. What am I doing wrong?

  - name: launch

      local_action:

        module: ec2

        region: us-west-2

        keypair: xxxxx

        group: "{{ my_groups }}"

        instance_type: t1.micro 

        image: ami-xxxxxx

        wait: yes

        wait_timeout: 3500

        count: 2

        instance_tags: '{"Name":"stuff"}'

      register: ec2

and set my_groups as:
my_groups: ['mygroup1', 'mygroup2', 'mygroup3']

My guess is it has something to do with the quotes but if i remove it, I get an YAML complaint, I've tried it a number of different ways without success. Any ideas?

Thanks!