Currently this isn't an option with CoalaWeb Traffic but I have just added it to the feature request list.
I'm just finishing up a couple of new releases for some of my other extensions and then it will be back to Traffic for some code improvements and new features so I will look into the possibility of a cookie for this purpose.
Hi! I'm Steve the founder and head developer of CoalaWeb design studios. I'm an avid supporter of open source projects and the GPL license.