Extend dynamic sentenceEmbedding vocabulary?

I really like the new sentenceEmbedding API and would like to use it in a project. However, how would you deal with situations in which there is specific vocabulary that the model most likely had not seen in its training corpus.

For instance, an app that allows you to answer rule questions for board games with vocabulary specific to the game (eg. fanatasy/sci-fi/...).

Is there any way to extend or use the transfer learning approach to "fine-tune" the model and extend vocabulary with a custom corpus?