I guess you can use Conditional around your Ad code. An example will be,
Code:
<if condition="!is_member_of($bbuserinfo, X,Y,Z)">
Google Ad Code
</if>
Here X,Y,Z are the UserGroup IDs which do not see the Ads, you should change it to yours. You can use it in your Ad location template.
A better way may be to use some Ad Management Mod though, If you are not experienced enough.
Shishir
EDIT: I am always late.

I thought none is replying so gave my shot.