how to use smart-selects for a many to many field against a foreign key selection in django admin?

[skalluri01]

In the below scenario, how to display the subcategories of the selected category only in admin site? Chained ForeignKey/ Chained Many to Many doesn't provide such use case..

class Category(models.Model):
name = models.CharField(max_length=20)

class SubCategory(models.Model):
name = models.CharField(max_length=20)
category= models.ForeignKey(Category)

class Course(models.Model):
name = models.CharField(max_length=20)
category= models.ForeignKey(Category)
subcategory=models.ManytoManyField(SubCategory)