First of all, I generally agree with the Admin #2 approach. To me, this group ranks 3rd in the priv hierarchy (host > admin > admin 2). This isn't what I understood you wanted. What I think you are asking is for a way to drop on a module that prohibits Admins from editing a page. Basically, you want a host level page that can be viewed by all (or specified groups) and only edited by hosts. Is that right?
Presuming my assumption is right, I thought I'd try it out. I hadn't really thought about the PA approach, but when it was suggested I couldn't think of any reason it couldn't be done. So I tried. I built a module that has no interface but simply runs some sql to adjust the priv settings. I get close. For some reason, though, if the page is located outside the host structure (child of host), it automatically resets the page privs everytime you update Settings. When it does this, it grants Admin edit access again. I'm not sure why that is. Maybe someone can figure that out. The approach I took was to mimic TabPermission settings for host pages and then add a View priv to All Users. I can't think of why this isn't possible, but I can't get it to work.
In my environment, we want control over what pages an Admin has access to, but we still use the regular Admin group. All we're really doing is removing and adding pages under the Admin tab.
It seems like when you take the page out from underneath Host, something happens behind the scenes that says "Hey, Admins should be able to edit me" and it makes the priv adjustment. I'll keep trying because I'm puzzled by not being able to do something (even if it's not the right approach). For now, you may be stuck with the Admin 2 method. That should work, just don't ever put someone in the built-in Admin role.
One other thing you could do is create a PA like I was trying that automatically sets edit privs to your Admin 2 role. If you set this module on all pages it should take care of the issue of an Admin 2 person forgetting to assign Edit privs to himself.