Different cart templates for multi vendor site?

[Nocturnaloner]

I believe this is still technically multi vendor, NOT multi store - I want to have my add to cart and checkout buttons show carts that have a different appearance when customers checkout at different parts of the site.  So www.demostore.com/girls/store-home/user/editaddresscheckoutBT has one template, and www.demostore.com/boys/store-home/user/editaddresscheckoutBT has a different template.  Actual final checkout is external, so SSL is not a factor.  How can this be accomplished?