I'm pretty sure you can use
/qn even if LIMITUI is defined.
And you could populate the TRANSFORMS property in the Property table to point to an external transform; if you're interested, Chapters 9 and 19 of
Administrator's Introduction to Application Repackaging and Software Deployment using Windows Installer cover these topics—transform packaging options, command-line switches, and such like—in a fair bit of detail. (For information, see
www.installshield.com/ispress.)