how to have my second wordpress install point to the default install

I have two different themes on my domain the first install is in the root folder and the second install is in a folder called secure. the second install is for a sales funnel while the first is my blog the question i have is when a user goes through the funnel an email is sent with a link back to the domain/secure/ url which does not exist, it should go to domain/ but there is no way to change it that I can see. i tried to change the wordpress site url and home url and it made all the pages in the /secure/ install point back to the root home page but i was able to fix it by modifying functions.php.
how can I set it so that the second install’s home page points to the root folder instead of the secure folder but keep all the pages in /secure/ still accessable? or in other words how do I point only domain/secure/ to domain/
hope that makes sense