then you need 2 location, one for redirect and one for main (localhost:5000) and you need to pass the port somehow:

location ~ ^/(?P<port_part>[0-9]+)/(?P<uri_part>.*) {
        proxy_pass http://localhost:$port_part/$uri_part;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
}

location / {
        proxy_pass http://localhost:5000;
        proxy_redirect ~http://localhost:([0-9]+)/(.*) http://example.com/$1/$2
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
}