How can i get custom API urls for different users.

Question

I am developing an office 365 add-in for my organisation. The use of this add-in is to fetch the document and send the document data to the backend server via Rest Api.
I am able to do this but the problem is we have clients that have private instances of our application with different hostnames. instead of developing these add ins for individual clients is there a way to alter the api hostname that the application to post the document data. Something like a configuration page while admin installs the add in for the entrire organisation or accessing a value from manifest file?