Set active directory groups as administrators

We have our macs bound to active directory and this is how our students log into them.

I can manually add active directory groups as administrators, however I am trying to find a unix command I can send to do this through ARD

I have found this on the apple website

dseditgroup -o edit -n /Local/Default -u localadmin -p -a networkuser -t user admin

we have an ad group called supportgroup, we want this to be admins on the macs.

Trying it with ARD there doesn't seem to be a way to include the local admin account password in the command so it fails due to lack of authentication. However trying it on the actual mac itself doesn't even seem to work, when i do this

dseditgroup -o edit -n /Local/Default -u technical -p -a mydomain\supportgroup -t user admin

I thought this might because this will only do users and not groups, so i tried it with a single (AD) user account and this wouldn't work either, keep getting the error message

Error locating specified node

So 2 questions

1. Is there a way to include local admin password in the command so this can be done by ARD

2. Am I doing this command wrong?

Hope someone can help