I am trying to use inlineformset_factory to generate a formset. My models are defined as:

class Measurement(models.Model):
    subject = models.ForeignKey(Animal)
    experiment = models.ForeignKey(Experiment)
    assay = models.ForeignKey(Assay)
    values = models.CommaSeparatedIntegerField(blank=True, null=True)

class Experiment(models.Model):
    date = models.DateField()
    notes = models.TextField(max_length = 500, blank=True)
    subjects= models.ManyToManyField(Subject)

in my view i have:

def add_measurement(request, experiment_id):
    experiment = get_object_or_404(Experiment, pk=experiment_id)
    MeasurementFormSet = inlineformset_factory(Experiment, Measurement, extra=10, exclude=('experiment'))
    if request.method == 'POST':
        formset = MeasurementFormSet(request.POST,instance=experiment)
        if formset.is_valid():
            formset.save()
            return HttpResponseRedirect( experiment.get_absolute_url() ) 
    else:
        formset = MeasurementFormSet(instance=experiment)
    return render_to_response("data_entry_form.html", {"formset": formset, "experiment": experiment }, context_instance=RequestContext(request))

but i want to restrict the Measurement.subject field to only subjects defined in the Experiment.subjects queryset. I have tried a couple of different ways of doing this but I am a little unsure what the best way to accomplish this is. I tried to over-ride the BaseInlineFormset class with a new queryset, but couldnt figure out how to correctly pass the experiment parameter.