Hi @whynot,
I was looking around to find an answer to your question, and it seems that another user was able to get this working, although they reported at first the bedrock hosted model did not appear at first but then it did appear 
They mention that they are using the AmazonBedrockFullAccess full access policy. Check if you have the same level of permissions and then maybe give the app a nice hard refresh to see if the model option will be re-fetched and populate 