default_transport in master.cf

[dave.postfix-us...@mtfbwy.cz]

Hi, I'm trying to change the default_transport directive in master.cf 
but it doesn't work:

1.2.3.4:smtp      inet  n       -       n       - -       smtpd
    -o default_transport=smtp_redir
smtp_redir      unix  -       -       n       -       - smtp
    -o smtp_bind_address=4.3.2.1

I have multiple smtpd instances on different IPs and I need to use 
different outbound IP address for some of them. I know I can use 
multiple Postfix instances but I'd rather avoid that - I realy need to 
change just the IP addresses.

Thanks,

Dave.