syntax for using function parameter in to_char

I am trying to write a function that will take a big int as a paramter and
return a formatted date string. The dates in the system I am using are all
stored as bigint values ( based Java EPOCH ) to I need this function to
make some sense of the date.

Here is my code:

CREATE FUNCTION java_date( bigint ) RETURNS text AS '
select to_char(\'epoch\'::datetime + \'$1 seconds\'::interval,
\'dd/mm/yyyy hh:mi\') as RESULT
'
LANGUAGE 'sql';

The problem seems to be that the $1 in the to_char function is not getting
parsed with the actual value of $1.

If I execute the following from the command line, I get the expected
response:

=> select to_char('epoch'::datetime + '1012437127 seconds'::interval,
'dd/mm/yyyy hh:mi');

to_char
------------------
30/01/2002 06:32
(1 row)

All I am trying to do is move the functionality of this SQL statement to a
function so I can easily reuse it.

Any help would be appreciated.

Kevin Barrett