Probably the easiest way to handle this would be to make symbolic links from the vanity directories to the actual directories. SSH into the server, cd into your web site's root directory and type:
ln -s original venue1
Then, in your PHP code, you can log the directory path and this will provide an idea of how much traffic each URL gets. (If you want to get fancy, you can even check the directory path and use that to customize the look of the site - or even offer special discounts and prices).
When the user visits the directory /venue1, the URL bar will stay in venue1 for the whole session (links will work as long as you always use relative URL's in your HTML) so no .htaccess or site modification is necessary. In fact, if you did this with .htaccess rewrite rules, you might have trouble with determining which vanity URL they were using - and you might have trouble with making links work.