I have done this before and have written about it but could not lay my hands on where. I know that someone has told me that they had installed the oracle software doing a custom install and not choosing the httpd install then then restarted the OUI as a differnt user and simply just installed apache from the Oracle CD and it worked fine. I have not tested this method myself, maybe I will!. The way I did it was by creating a seperare apache user and group and, well doing what Roger Shrag describes in his paper Installing and Configuring Oracle9i on the Solaris Platform. This is a excellent paper. He tells how to create an apache user, how to install Oracle, then stop apache, change the ownership of the files and then restart apache as the new user.
Great paper and well worth reading.