How do I do backspace in variable pair?

I have a module called netwerk that has a member list tag, part of this list is the category tag pair. I would like to allow for a backspace parameter in the inner tag pair. How would I implement this?

The template would look like this:

{exp:netwerk:member_list}
    {member_name}
    {categories backspace="1"}
        {category_name},
    {/categories} 
{/exp:netwerk:member_list}

Is it possible to do this?