can you change an FK constraint from NOT DEFERRABLE to DEFERRABLE

Hello. Is it possible to change an FK constraint from NOT DEFERRABLE
(the default) to DEFERRABLE without dropping and re-creating it? One idea
that came up was to create a parallel set of constraints which perform
the same checks as the existing ones as DEFERRABLE (and then drop the
old set), but the objection there was that it'd lock the tables during
the initial check.

We're having a fairly serious deadlock issue and the thinking goes that
Tom's suggestion here

http://www.webservertalk.com/archive139-2004-8-364172.html

to defer FK checks until transaction commit would maybe help. Right now
we can't try this because all the FK checks where created with default
settings. We'd like to avoid taking the database down for recreating
foreign keys.

Regards,

Frank