Currently only available in Creation Mode, and will be adapted for Survival Mode in a future update, it will consume cubes from the player's backpack.
There are still some issues with the thrower, I've been debugging it for a long time and I still can't get the trajectory of the thrower to match the trajectory of the snowball.
If you have the ability to implement this please modify the hole-filler/behavior_pack/entities/base.json file and let me know and I'll put you on the list of contributors, thank you very much!