The easiest way to do this would be to not use “relative to camera”, but instead position the sprites on every frame yourself! We have some camera blocks in the scene category that are useful for this.
One note: this won’t work inside an “on game update” because the camera doesn’t get updated until after that code gets run. Luckily, I added a block to @jwunderl’s jwunderl/arcade-sprite-util to make this easier:
Here’s a link to the example: https://makecode.com/_9FkEaFey5eC9