How to pass a queryset to a ModelChoiceField using a self.field_value in Django ModelForms

I could explain the whole thing to you but I guess a code speaks clearer than words so:

  class Skills(models.Model):
        skill = models.ForeignKey(ReferenceSkills)
        person = models.ForeignKey(User)

class SkillForm(ModelForm):
    class Meta:
        model = Skills
        fields = ( 'person', 'skill')
    (???)skill = forms.ModelChoiceField(queryset= SkillsReference.objects.filter(person = self.person)

I'm just guessing at how I can do it. But I hope you guys understand what I'm trying to do.