I know this is an old one, but I was trawling through the forums and I thought I could at least post the method I have used to do this.
To achieve a similar 'use-case' what you were after, I deployed the Agent using the GPO method via a simple batch script (in its own GPO) and applied it to the top level OU. Then to target (or exclude) workstations I applied item level targeting on the Policy to include/exclude workstations by name, or IP range, or ... Pretty much anything I needed to!! I even think you can do it by OS, RAM and even No. of CPU's. That item level targeting can get pretty crazy, but it's very useful in certain scenarios much like this one.
Anyways, I hope to god you got it figured by now...I'm just not a fan of seeing unanswered questions here, especially when they are good ones that I know I can answer correctly, of course!!
Take it easy,
To achieve a similar 'use-case' what you were after, I deployed the Agent using the GPO method via a simple batch script (in its own GPO) and applied it to the top level OU. Then to target (or exclude) workstations I applied item level targeting on the Policy to include/exclude workstations by name, or IP range, or ... Pretty much anything I needed to!! I even think you can do it by OS, RAM and even No. of CPU's. That item level targeting can get pretty crazy, but it's very useful in certain scenarios much like this one.
Anyways, I hope to god you got it figured by now...I'm just not a fan of seeing unanswered questions here, especially when they are good ones that I know I can answer correctly, of course!!

Take it easy,