You can manually add the member(s) to a user group with enhanced permissions, manually apply a user group promotion, or edit the member(s) permissions directly.
So in relation to allowing 1 user to bypass the "2 post minimum" requirement for posting URLs, I found how this restriction is currently set up:
Given this, I don't think creating a user group with enhanced permissions will work. The permissions system doesn't have the "Allow URLs" yes / no option with "fewer than [ ] posts" (it really should! would be an amazing anti spam feature and we wouldn't have to jimmy rig something like the above.