Alex Gorbachev has posted a step-by-step guide on how to do just this here. And if you missed his Installation Guide for Oracle 10g on Mac OS X, you can find that here.
As he stated, the workaround is not a very secure thing to do; however, if you're just using it for local development, there should be no major issues. You have been warned.
In any case, I did have an issue with the code that he had posted to disable the security on XDB. After some searching around, I used the following instead:
A couple other notes: you'll have to also copy the images over to the database via XDB. You can map this drive via Mac OS X and then just copy the images over via the finder.
-- Get the current configuration
configxml := DBMS_XDB.cfg_get();
-- Modify the configuration
-- Update the configuration to use the modified version
To do this:
1) From the Go menu in the Finder, select Connect to Server...
2) For the Server Address, enter: http://localhost:8080 and click Connect.
3) When prompted, enter XDB for the user and the corresponding password.
At this point, you should see the localhost volume on your desktop. Simply create a top-level directory called i and then copy the APEX images folder into that directory, and you should be good to go with APEX on Mac OS X!