I assuming using Policy - require installation - and can change the frequency of the agent to check for policy should work?
Definataly. Be sure to use a 'pure' policy, not the policy-supported push. Start it once and never restart it again. It will stay active.
2 remarks. Don't worry if you don't see your new target immediately in the task after you add it to the OU. First of all, the Scheduler Service on the Core resolves LDAP queries by default every hour (Configure - Services - Scheduler, in a Console on the Core Server), second, the client asking for the policy will always tell the server 'who' he is. So it will automatically see which tasks are targeting that device (or user). This you can check in the local policy.sync.exe.log.
I will give it a try..