PARTIAL, DEFERRABLE UNIQUE CONSTRAINTS

Hello,

I need to create a deferrable,unique partial constraint (using a WHERE clause) on my table, which in addition should also be deferrable. AFAIK deferrable constraints are just creatable with

ALTER TABLE demand ADD CONSTRAINT unique_salesorderitem_id
UNIQUE (salesorderitem_id) DEFERRABLE INITIALLY DEFERRED;

but here I miss the WHERE clause. Using the CREATE INDEX notation like this:

CREATE UNIQUE INDEX idx_demand_salesorderitem_id_of_parentdemands
ON demand(salesorderitem_id) WHERE parentdemand_id IS NULL;

I cannot specify the deferability (is that a word?). I am Using PostgreSQL 9.1. Is there any way around this?

Regards,
Daniel Migowski