I am aware of his living conditions there, but I am curious as to how his stay on the island was enforced. I'm sure his person was kept under guard, but did the island have a permanent naval presence? If not, what would stop a group of Bonapartists taking a warship or even an armed merchant vessel to go pick him up? Surely the island's garrison could be overcome. Did any such attempt ever occur?
After being stationed in India, a young Arthur Wellesley stopped on a small island in the South Atlantic that was a port for the East India Company called St. Helena, noting that it was isolated but beautiful. When the Emperor surrendered to Wellesley, this island came to the British general's mind as an ideal location.
As a result, the British government would take control of the island and place Sir Hudson Lowe with a small contingent of British soldiers (and the families of any officers), leaving Lowe as the governor of the island. As a port of call, it would have some protection and one of Lowe's responsibilities was to keep the island well stocked with provisions, thus ensuring a consistent amount of British shipping and military ships would pass through.
Further, once Napoleon was defeated, there was no more attempt to place Napoleon or any sort of Napoleonist groups into power as the trial of Michel Ney, a travesty of justice, made a point to ensure that he was an example for those that sided with Napoleon during his return. There would be fond feelings for the Napoleonic era but never anything that would push for the return of Napoleon or Napoleon II as a power, it wouldn't be until the election of Louis Bonaparte as president that there would be an active Bonapartist party in French politics.