You could perhaps use a reducing agent and a solution of an easily reduced gold salt.
Hydrazine hydrate is used in a reaction to prepare ultrathin mirror and resistant surfaces on the insides of glassware from washing with a metal salt solution and the hydrazine hydrate.
Alternatively, you could attempt using ascorbic acid, as it is somewhat of a decent reducing agent, it will reduce copper salts, and less reactive metals, in aqueous solution, to the finely devided metal, so I would not be surprised at all if you could adapt the process to produce a fine layer of metallic gold upon a nonconductive surface.