Deferrable, case-insensitive unique constraint

Is it possible in PostgreSQL to create a deferrable unique constraint on a character column, but case-insensitive?

Let's assume the following basic table:

CREATE TABLE sample_table ( 
   my_column VARCHAR(100)
);

If deferrable constraint is not needed, it is as simple as creating unique index with function, e.g.:

CREATE UNIQUE INDEX my_unique_index ON sample_table(UPPER(my_column));

Deferred constraint check requires creating the constraint explicitly, e.g.:

ALTER TABLE sample_table 
 ADD CONSTRAINT my_unique_constraint UNIQUE(my_column)
 DEFERRABLE INITIALLY IMMEDIATE;

And unfortunately it is not possible to use arbitrary functions in unique constraint.

One possible workaround would be to create additional column with the same content as my_column, but upper case, updated via a trigger after each update/insert, then create a deferrable unique constraint on this artificial column. This, however, sounds like a really ugly hack.

Alternatively, it should be possible to use CREATE CONSTRAINT TRIGGER and manually check for case-insensitive uniqueness (of course a regular index would still be necessary). This sounds a bit overcomplicated for such a simple (and popular, I suppose) requirement.

Is there any simpler and/or more elegant way around this limitation?
I am using Postgres 9.1 at the moment. But solutions for newer are welcome.

You can circumvent the restriction by using the special type citext provided by the additional module of the same name. Quoting the manual:

The citext module provides a case-insensitive character string type, citext. Essentially, it internally calls lower when comparing values. Otherwise, it behaves almost exactly like text.

It addresses your case exactly. Run once per database:

CREATE EXTENSION citext;

Then you can:

CREATE TABLE sample_table ( 
  my_column citext
, CONSTRAINT my_unique_constraint UNIQUE(my_column) DEFERRABLE INITIALLY IMMEDIATE
);