Effectively, iOS only supports well-known. If an iOS device cant connect via well-known it will allow the user to enter a complete principal address, BUT thats only AFTER displaying an error message to the user, at which point most users will give up.
However, the redirect occurs after authentication, so as long as you're able to authenticate at the root (eg with a username scheme that incorporates the sub-site, like 'appOne:brad') then you should be able to do it. Alternatively, as mentioned above, just use subdomains.