variable-length arguments passed by reference... how?

I want to create a function similar to the MySqli extensions' mysqli_stmt_bind_param() function. I assume that this function takes its arguments passed by reference. Now, I know how to do variable length argument lists in a function with func_get_arg(s) but how do I tell it that they are to be passed by reference? I'm using PHP5 and I want to stick by the latest recomendations..