You would need a script to do that... which you could do, but it would be contingent on the organization of the data in your JSON structure. There are other options, though... like the TableToTable script that provide a way to use existing tables from outside Roll20, paste them into a particular handout, and have them be processed into rollable tables. Here is a series of videos on using the script. If you really do want to move forward with processing JSON information, post back and we can pass on resources that would help in the development of a dedicated script for your project.