Add argument to show cases assigned to user

I thought this was possible but I see that is not. What I'm trying to do is create a block to show on the user's page and it would be something like "cases assigned to this user".

We only need the argument to define the cases that are assigned to the user, we already have a filter to do this but we don't have an argument. I'm not an expert in views, I'll see what I can do and try to make a patch but I would appreciate some help.