Best way to prevent links from showing to guests?

[Razasharp]

Is there a simple solution to prevent links from showing to guests in posts?

Not worried about calendar, or print view or search or signatures, just the links in posts. I don't want it to effect post-caching either, hence none of the current mods are suitable.

Can I directly modify the php code to add a conditional to the bb code URL? Or will that not work?

Any help appreciated!