Not as json, but you can email a chunk of historic datapoints to the bot and it’ll try to do the right thing. You may need to go to the settings tab to change the goal’s start date in order to see the history.
subject: user/goal
format per line: yyyy mm dd value "optional comment"
Probably best to do this during goal creation with a flat commitment line; otherwise you risk insta-derailing yourself. You can use the graph editor to approximate your historical commitment later.