Hi,
If you are using file-based installation, you can install as non-root user and create domains as usual. You can use asadmin command available at <AS_INSTALL>/bin to do this.
ex: ./asadmin create-domain --domaindir /tmp/justfortest --adminport 4850 --adminuser admin domain_nonroot_test
Did you face any problem doing this in non-root. Unless you have write permissions in domaindir, you won't be facing any problem.
Hope this clarifies your question.
Thanks,
-Balaji.