One thing that I could think of would be to make the admin a member of both the admin usergroup and another usergroup (registered users for instance). Then change the display usergroup to 'registered user.' You need at least 2 usergroups selected for 'display usergroup' to be shown. So after you select 'registered users' as well, you may need to reload the profile. You'd do this on the admin's profile in the AdminCP of course.
But, if you allow mods to 'view entire profiles (but not edit),' they could still see that the admin is a member of the 'admin' usergroup in the ModCP. If you want to change that, you'd change that option (Can View Whole User Profile (but not edit) = no) for all the moderators in their mod permissions. Other admins could still see though.
If there is another way, I'd like to know as well.