Filtering on a Window function in Django

I have the following model:

class Foobar(models.Model):
    foo = models.IntegerField()

And I figured out how to calculate the delta of consecutive foo fields by using window functions:

qs = Foobar.objects \
    .annotate(
        delta=F('foo') - Window(Lag('foo'), partition_by=F('variant'), order_by=F('timestamp').asc())
    )

Now I only want the records from this where delta is negative:

qs.filter(delta__lte=0)

But as you might expect, this gives an error:

django.db.utils.NotSupportedError: Window is disallowed in the filter clause.

How can I do this filtering with the Django ORM?