We can simplify by adding a second pointer in the header:

template <typename Data>
struct LListHeader {

  LListNode<Data>* first;
  LListNode<Data>* last;

  LListHeader();
    ⋮

template <typename Data>
void LListHeader<Data>::addToFront (const Data& value)
{
  LListNode<Data>* newNode = new LListNode<Data>(value, first);
  first = newNode;
  if (last == NULL)
    last = first;
}

template <typename Data>
void LListHeader<Data>::addToEnd (const Data& value)
{ 
  LListNode<Data>* newNode = new LListNode<Data>(value, NULL);
  if (last == NULL)
    {
      first = last = newNode;
    }
  else
    {
      last->next = newNode;
      last = newNode;
    }
}