Now you actually can do it!
You’ll need to create a block that contains an asset field
(an example block bellow)
Then, editing the structured text field on your model, you must include under validations the image block as one of the blocks allowed:
After saving, you may go to the record of the structured text, and there you’ll be able to add your images by using /Image block (or the name of the block you created)
You can add how many image blocks as you like, and also add other fields other than the Single asset field to your block if you desire (even other blocks!)
Hope that makes things clear