Вы получите виджет Admin FileField вместо стандартного с 5 дополнительными полями.
views.py
MySpecialFormset = inlineformset_factory( MyParentModel,
MyChildModel,
form=MyChildModelForm,
extra=5)
formset = MySpecialFormset(instance=myparentmodelinstance) #add request.POST and request.FILES if used on the POST cycle
forms.py
from django.contrib.admin.widgets import AdminFileWidget
class MyChildModelForm(forms.ModelForm):
class Meta:
model = MyChildModel
def __init__(self, *args, **kwargs):
super(MyChildModelForm, self).__init__(*args, **kwargs)
self.fields['my_file_field'].widget = AdminFileWidget()