Referral system like dropbox one

Question

I want to implement a referral system to my system where registered users can invite other people by emailing their referral link (i.e. /register/referral/123123/) just like dropbox one ( and if a person signs up, the referrer gets additional bonus. Currently I have implemented it this way: Models:

class UserReferral(models.Model):
STATUS_INVITED = 1
STATUS_ACCEPTED = 2
STATUS_EXPIRED = 3

STATUS_CHOICES = (
    (STATUS_INVITED, 'Invited'),
    (STATUS_ACCEPTED, 'Accepted'),
    (STATUS_EXPIRED, 'Expired'),
    )

referrer = models.ForeignKey(User, related_name='referrers')
referred = models.ForeignKey(User, related_name='referred')
number = models.IntegerField()
status = models.IntegerField(choices=STATUS_CHOICES, default=STATUS_INVITED)

class Meta:
    unique_together = (('referrer', 'referred'),)

def __unicode__(self):
    return 'User %s referred %s' % (self.referrer.get_full_name(), self.referred.get_full_name())

@property
def referral_expired(self):
    expiration_date = datetime.timedelta(days=settings.ACCOUNT_ACTIVATION_DAYS)
    return (self.status == self.STATUS_ACCEPTED or
                   (self.referred.date_joined + expiration_date <= datetime_now()))

Views: This view is used by the registered users to send out new referral invites

@login_required
def invite_friends(request, template_name='accounts/invite_friends.html'):
if request.method == 'POST':
    form = InviteForm(request.POST, user=request.user)
    if form.is_valid():
        emails = form.cleaned_data['emails']
        for email in emails:
            try:
                user_referral = UserReferral.objects.get(referrer=request.user, referred__email=email)
            except UserReferral.DoesNotExist:
                random_username = ''.join(random.choice(string.ascii_uppercase) for x in range(6))
                user = User.objects.create(username=random_username, password=email, is_active=False)  # Dummy user to be overridden
                user_referral = UserReferral.objects.create(referrer=request.user, referred=user, number=random.randint(10000, 99999))
                send_mail('accounts/notifications/invite_friends', recipient_list=[email],
                        context={'user': request.user, 'number': user_referral.number})

        messages.add_message(request, messages.SUCCESS, "Invites are sent.")
        return redirect(reverse('profile_dashboard'))
else:
    form = InviteForm(user=request.user)
return render(request, template_name, locals())

This is the URL where referred users can register, it basically calls the original register function with referral code, and check in the register view if the referral code is present, if so, it fetches the referred user instance from the UserReferral instance and populates the user data from the register form and saves that new user.

def referred_signup(request, referral_code):
user_referral = get_object_or_404(UserReferral, number=referral_code)
if user_referral.referral_expired:
    raise Http404
response = register(request, referral_code=referral_code)
return response

So I create the dummy inactive 'referrer' User account every time the new invite is generated. And when on the registration time, I populate the names, password etc. from the user input form, and change the UserReferral instance status to ACTIVATED. Is there any better alternative to this one?