Using domains for case insensitivity

Hi all,

A while back I asked about creating a case insensitive postgresql. Tom, 
at the time, suggested I create a case insensitive type instead.

I am now trying to go that route, and am wondering whether domains will 
provide a shortcut for me. As far as I understand the task at hand, I am 
quite capable of using all of the existing varchar functions for input, 
output, storage, conversions and so on. The only thing I need to 
override is the comparison functions (and the resulting index creation, 
of course).

According to the docs, domains are not meant for that purpose, but for 
changing constraints of a type. Is it possible to define a domain that 
will have the same defaults and constraints as the base type, but will 
have different comparison functions? Will that provide me with what I need?
            Many thanks,
                        Shachar

-- 
Shachar Shemesh
Lingnu Open Source Consulting ltd.
http://www.lingnu.com/