I had similar issues, but managed to get it working.

Step 1:

Download and start an LFS server (if you haven't already done so), such as https://github.com/git-lfs/lfs-test-server (Don't use this one in production.)

Step 2:

Correctly set up the LFS server URL for your repo, as described here: https://github.com/git-lfs/git-lfs/wiki/Tutorial#lfs-url

In my case, running the following in my working copy folder was enough:

git config -f .lfsconfig lfs.url http://username:password@localhost:8080
git add .lfsconfig

Replace username and password by your desired credentials, and localhost:8080 by your Git server URL.

You can run git lfs env to verify your results.

Step 3:

Set up your LFS_ADMINUSER and LFS_ADMINPASS environment variables as described here: https://github.com/git-lfs/lfs-test-server#running

Then, you should be able to visit http://localhost:8080/mgmt (or wherever your LFS server is running) in your browser and add your credentials.

The results look promising:

C:\Users\Nick\Desktop\WorkingCopy\Repo>git push origin master
warning: current Git remote contains credentials
warning: current Git remote contains credentials
Git LFS: (1 of 1 files) 6.72 KB / 6.72 KB
Counting objects: 3, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (3/3), done.
Writing objects: 100% (3/3), 428 bytes | 0 bytes/s, done.
Total 3 (delta 0), reused 0 (delta 0)
To C:/Users/Nick/Desktop/WorkingCopy/../Repo
   309629f..7fe106d  master -> master

The lfs-content folder of the LFS server now contains a file with the exact size of the added file.