You could also spray each Christmas ball with spray glue adhesive and roll each around in a dish of rock salt ( one box can be purchased for $1.20)
I read somewhere that you could use spray adhesive and then sprinkle sugar on, don't know how permanent that would be.
Crafts stores sell fake snow in a jar it has a frosting consistancy. you spread it on as thick or thin as you want and you can smooth it out or leave it a little bumpy. it air dries hard It isn't that expensive I have used it with my Girl Scout troop. and a small jar can go a long way.
When I posted my suggestion about packing peanuts, the heading of the request said snow globes, hence the suggestion about floating the bits. You could still crumble/cut up the foam and dip your ornaments in them after putting glue on the glass balls.
Could you use packing peanuts or other styrofoam cut into little bits? Depending on what liquid your globes are filled with, they should float.
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