XOwiki sets them here, if they aren't already set:
http://cvs.openacs.org/cvs/openacs-4/packages/xowiki/tcl/xowiki-www-procs.tcl
Beyond that, such as how to set the values before the code reaches here, I'm not sure. All the local versions of xowiki I have running are from before this code was added. I won't be updating for a few more months.
Unless someone else steps in, I guess you could remove/comment out the offending code.
cheers,
Torben
