I think you are pretty much out of luck unless Jails get ported to Mac OS X (it wouldn't be a bad idea!). chroot is available, but no where near Jails in terms of functionality.
virtual hosts might work for multiple domains, but you can really have a custom apache install for each. (i.e. perl for one site, php for another and python for a third) unless you don't mind having all three modules running at once. This of course is a bad practice as it increases the attack surface. Jails solve this and allow users, but alas they are not available in Mac OS X.
