The only solution is to use "flo=true" URL parameter in all WebLink URLs, which prevents iCode from being included in the URL and forces cookie to be deleted when browser window is closed.
Since Event Reg doesn't support "flo=true", I am not aware of a good solution for this problem in the Eveng Reg module. I would like to see all WebLink modules support the "flo=true" option and have a logout button within the WebLink window.
Maxim