LDAP or NIS is the Right Solution -- it's really not that complicated, and you should take a day and learn both (figure about half a day each to get the basics. Less if you buy the O'Reilly NIS book & LDAP book.
The big advantage here is you can centralize some accounts (administrative access/support users), authorize others on a per-jail basis, and still have local users on specific machines.
If you're really dead-set against LDAP or NIS the next best thing is to use Puppet, Chef, radmind, or similar to update the
group files -- you can automatically synchronize the authentication/authorization files as part of a site-wide deployment process.
Automatic deployment tools have their own complexity issues, but also bring a number of benefits which may make them appropriate for your environment
The next step down is a cron job on the host system that copies standard
group files to each jail at a set time. This is the simplest solution and works very well, though it is only a very small step up from copying the files yourself manually.