Variadic functions and name

Hi
I am plaing with functions with variable number of arguments. I found an
example of such a function at
http://www.depesz.com/index.php/2008/07/31/waiting-for-84-variadic-functions/
.
Up to this point everything is clear, all the parameters are of the same
type and function works.
But I wan't to simulate named function arguments (as in oracle funct_name
(arg1 => test) - syntax is not so important). I also found another examle (
http://archives.postgresql.org/pgsql-patches/2008-01/msg00103.php)
Syntax in this example is as follows:
select json_object('value1' as name, 'value2' as surname);
Function declaration :
json_object(anyparams)

I am trying to write similar function in plpgsql but all I get is 'type
anyparams does not exist'.
Is it possible?

--
Regards, Adam Wałach