Make your group, and specify the rules for dynamic members, and press OK.
Again go to add/remove contacts for this group, and in the static members section, press contacts button, and from the "select from" drop down list box, select Groups, and select the same group name.
Now you can select the first contact, and shift+click on the last contact, and add all of them as static members to this group. Then you can remove the dynamic membership rules if you want.
