saving an m2m field in one API call

gistfile1.py

# models.py
class Subscriber(models.Model):
    country = CountryField()
    first_name = models.CharField(max_length=100, blank=True, null=True)
    surname = models.CharField(max_length=100, blank=True, null=True)
    email = models.EmailField()
    brands = models.ManyToManyField("Brand")

#forms.py
from django import forms

class SubscriberForm(forms.Form):
    brand = forms.CharField(required=True)
    email = forms.EmailField(required=True)
    country = forms.CharField(required=True)
    first_name = forms.CharField()
    surname = forms.CharField()

# api.py
from tastypie.resources import ModelResource
from tastypie.validation import FormValidation
from subscribers.forms import SubscriberForm
from subscribers.models import Subscriber
from tastypie.authorization import DjangoAuthorization
from tastypie.authentication import BasicAuthentication

class SubscriberResource(ModelResource):
    class Meta:
        queryset = Subscriber.objects.all()
        resource_name = 'subscriber'
        allowed_methods = ['post']
        authentication = BasicAuthentication()
        authorization = DjangoAuthorization()
        validation = FormValidation(form_class=SubscriberForm)