How to map one single file into kubernetes pod using hostPath?

I have one own nginx configuration /home/ubuntu/workspace/web.conf generated by script. I prefer to have it under /etc/nginx/conf.d besides default.conf

Below is the nginx.yaml

apiVersion: v1
kind: Pod
metadata:
    name: nginx
spec:
    volumes:
      - name: webconf
        hostPath:
          path: /home/ubuntu/workspace/web.conf
    containers:
      - image:  nginx
        name: nginx
        ports:
          - containerPort: 18001
            protocol: TCP                               
        volumeMounts:
          - mountPath: /etc/nginx/conf.d/web.conf
            name: web

While it is mapped as folder only

$ kubectl create -f nginx.yaml
pod "nginx" created
$ kubectl exec -it nginx -- bash
root@nginx:/app# ls -al /etc/nginx/conf.d/
total 12
drwxr-xr-x 1 root root 4096 Aug  3 12:27 .
drwxr-xr-x 1 root root 4096 Aug  3 11:46 ..
-rw-r--r-- 2 root root 1093 Jul 11 13:06 default.conf
drwxr-xr-x 2 root root    0 Aug  3 11:46 web.conf

It works for docker container -v hostfile:containerfile.

How can I do this in kubernetes ?

BTW: I use minikube 0.21.0 on Ubuntu 16.04 LTS with kvm