How to enable remote access for another account on Mac remotely via SSH?

I have admin rights at a remote Mac computer. I can access it via SSH. The Mac has another user account, which doesn't have remote access. How can I remotely (via SSH) enable remote access for the other account?

SSH access by users is controlled by the local copy of Directory Services. (Controlled using dscl)

First off run dscl . list /Groups | grep 'access_ssh'. If the returned value says com.apple.access_ssh-disabled then all users have SSH access. If not, then we need to give the user access.

To add the user you need to run:

sudo dscl . append /Groups/com.apple.access_ssh user USERNAME

(replace USERNAME with the short username of the user) as well as:

sudo dscl . append /Groups/com.apple.access_ssh groupmembers `dscl . read /Users/USERNAME GeneratedUID | cut -d " " -f 2`

(replace USERNAME with short username as well)

(The last bit is thanks to Reed Stoner on lists.apple.com)

To add/enable Remote Management for only specific users (Add VNC flags from ghoppe's answer if you want VNC):

sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -activate -configure -users short,usernames,seperated,by,commas -access -on -restart -agent -privs -all -allowAccessFor -specifiedUsers

Find out more by running sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -h

Based on Chealion's answer, I came up with this to allow ALL users to ssh in:

dscl . change /Groups/com.apple.access_ssh RecordName com.apple.access_ssh com.apple.access_ssh-disabled