We got segmentation faults while trying to install some rpms this way: rpm -Uvh --excludedir /usr kdetoys-1.1.2-2.sparc.rpm while /usr being mounted read-only. This behaviour is similar for all rpms where /usr is relocatable. The quick and dirty workaround is to use the following command: rpm -Uvh --relocate /usr=/tmp --excludedir /usr kdetoys-1.1.2-2.sparc.rpm which does exactly what we want: Omit all files of the /usr tree while installing an rpm-package.
Confirmed with latest rpm in rawhide: [root@ostrich-deluxe 6.2]# rpm -Uvh --excludepath /usr alpha/kdetoys-1.1.2-3.alpha.rpm --nodeps Segmentation fault
Fixed in cvs, will be in rpm-3.0.4-0.43. Thanks for noticing.