Captain Nemo by Kevin J. Anderson
The young Verne and his best friend Andre Nemo stow away on a ship bound for the high seas, but Jules' father catches Jules and forces him to come home in total disgrace. Nemo goes on to have all the adventures, battling pirates, fighting sea monsters, being shipwrecked, ballooning across Africa etc. Jules eventually turns these real life tales of his friend into his popular novels.