How to use a custom variable for the scheme in a rewrite rule in nginx

Is there a way to get nginx to treat a custom variable the same as it treats the $scheme in a rewrite rule? For instance:

rewrite ^/redirect http://example.com;
# and
rewrite ^/redirect_with_scheme $scheme://example.com;

will both result in a 302 redirect being sent to the client. However, this:

set $real_scheme $scheme;
rewrite ^/redirect_with_real_scheme $real_scheme://example.com;

will result in a server side rewrite to a file that doesn’t necessarily exist and then a 404 to the client. For what it’s worth, this:

set $real_scheme $scheme;
rewrite ^/redirect_with_real_scheme $real_scheme://example.com redirect;

will give the desired result of sending a 302 to the client. Unfortunately, I have a lot of redirects set up this way and I would rather not update all of them with the redirect directive if it’s not necessary.

If it’s helpful, I’m using Nginx 1.6.2.

events {
    worker_connections  1024;
}


http {
    include mime.types;
    server {
        listen       80;

        set $real_scheme $scheme;
        rewrite ^/redirect http://localhost;
        rewrite ^/redirect_with_scheme $scheme://localhost;
        rewrite ^/redirect_with_real_scheme $real_scheme://localhost;
    }
}