How to create specific bins out of a range

Hi,
I have a 8-digit binary number, and I want to create a bin that collects all combination of this numbers, but with 4 or less '1’s in it.
the full range is [0:8’hFF] but I want to exclude the numbers that has more than 4 '1’s in it.
is there any way to create such bins?
thanks!

In reply to Tzofia:

a: coverpoint x
{
bins count4[] = {[0:8'hFF]} with ($countones(item) <= 4);
}