Add additional argument to argument received from URL

I want to be able to add additional argument to argument I receive from URL. The argument I receive from URL is user ID (not current user). I want view add current user ID as second argument. I don't want to add a second argument as separate User: Uid argument then views will use select with AND (user.uid=1 AND user uid=9).
I want to add the argument to first argument like both arguments received from URL. In this case I hope view will use (user.uid=1 OR user uid=9) How can I do this?