Hello,
You can simply put the URL with subdirectory of your domain hosted on shared hosting package in redirect settings of domain (hosted elsewhere).
For example :
You have domain
Home - ABC.com hosted on shared hosting and you have
http://xyz.com hosted elsewhere and you want to redirect
http://xyz.com to http://abc.com/< subdirectory> , then you just need to put http://abc.com/< subdirectory> URL in redirect setting of
http://xyz.com
You can do this using control panel of
http://xyz.com or you can ask to do hosting provider of
http://xyz.com .