All this mod does is allow users from a pre-defined IP address to be able to sign up without email verification. For example, on a school forum, new users might not have access to email from the school, and it is likely using a particular IP or a range. This mod would allow them to sign up without verification while retaining the safety of verification for all other addresses. Also a demo isn't really possible as it only instant-activate for the IP specified in advance.

I'm new to this so please forgive me if these instructions are lacking or difficult to follow. Rogersnm helped me with making this hack, which was really only intended to fit my needs but I figured why not release it. The mod was made for 3.5.4, no idea if it works on different versions.

Anyway, onto the hack.
1) Download and make a backup of register.php
2) Open the file with your text editor of choice and search for the following:
3) Replace the next line with the following (where "XX.XXX.XXX.XXX" is the IP address you wish to allow):
4) Search for the following:
5) Replace the next line with (same deal with "XX.XXX.XXX.XXX"):
6) Search for the following:
7) Replace the line two above it ("if ($vbulletin->options['verifyemail']...") with:
8) Save, double check that you have a backup, upload (overwrite) and hope nothing went wrong.
Good luck to anyone who finds this useful!