Scripting thn_register

Has anyone had much success with scripting rhn_register?

I would like to run rhn_register automatically as a post-install 
step. We would liek to automate installs as much as possible,
and running rhn_register is not feasible.


This won't work for me:
rhn_register --nox --configure \ serverURL=https://server:8081/XMLRPC

I could use Expect to script it I suppose.

Another way of doing things is just to supply a
/etc/sysconfig/rhn/rhn_register and systemid  pre-configured as part of
an RPM at install time.
That sounds ok - but all systems will then have the same systemid.
Maybe will cause problems in the future?