Simply asking Bard in the right formatting works fine. Admittedly the formatting is a bit annoying. Asking for no preamble doesn't work, asking for no leader doesn't work, asking for no additional description doesn't work.

> Me: Please give me a 2 word JSON dictionary without first saying "Sure, here is the JSON" or a similar phrase. It's very important to me that I only get the JSON and no other words or phrases. > Bard: * > JSON > { > "word1": "hello", > "word2": "world" > }