What you _can_ do to help keep the registrations real is:
Use a nick registration delay, this makes it so a user has to be connected for X number of seconds before they can register.
# NickRegDelay <seconds> [OPTIONAL]
# Prevents users from regging their nick if they are not
# connected for at least X seconds.
NickRegDelay 30
And you make it required to give an email address during registration by using NSForceEmail. Use NSRegDelay to keep the flooding down as well as using NSMaxAliases to control the number of nicks in a group.
After all that you can restrict the number of registered nicks per email address by using:
# NSEmailMax [OPTIONAL]
# Module: ns_maxemail
#
# Limit the amount of registrations with the same email address to the
# amount given here. If set to 0 or left commented, there will be no limit
# enforced when registering new accounts or using /msg NickServ SET EMAIL.
#
NSEmailMax 1
After all that, it's still possible for someone to register alot of nicks pointlessly, but they would have to have a ton of email addresses as well have alot of free time on their hands to register them manually or write a script to do it.
As a side note, with NSEmailMax, I suggest setting it to 3 or 5 instead of 1. Many users register their bots nick and/or their away nick as well as their primary nick, so using 1 would make it harder for legitimate users ..