Westlaw requires the following database definition in config.txt:

Option DomainCookieOnly
Title Westlaw
URL http://www.westlaw.com/(the-rest-of-your-westlaw-url)
HJ legalresearch.westlaw.co.uk
HJ login.westlaw.co.uk
HJ www.westlaw.co.uk
DJ westlaw.com
DJ westlaw.co.uk
Option Cookie 

Please note that many functions of Westlaw will only function properly if you disable any pop-up blocker. For example, printing may not work if a pop-up blocker is active.