I think you'd be better off covering the whole plant with a clear plastic bag if you want to ripen figs. But it will delay dormancy so I'm not sure it's a good idea. For the cup to work all the processes necessary to ripen the fig would have to happen inside the fig. Since picked figs don't ripen I think it's unlikely that warming the fig on a cool plant will help a significant amount.
The original use was to allow the fig to dry on the tree in a wet climate, not ripen the fig.
