MikeyMikey, you can get latex surgical tubing at Home Depot right by yonge & hwy 7. I think its like 15 bucks for 10 ft., I guess if you did this, it might save you some cash, but I'm not sure it would work. I use this stuff to make my own paint grenades, just cut off a foot of it, then tie off one end of it, then get a small drill or dremel and make a hole (1 hole would be good enough, 2 holes you might be losing a lot of salt quickly), put the holes wherever you want the salt to come out of, so maybe at end of one side of the latex worm, after you did that, fill the thing with salt (easy to do with a syphon), if you don't have a syphon just put a bowl underneth your hands while filling, easier to refill wasted salt. Next, tie off the open end of the latex worm, and lastly, cut of most of the excess surgical tubing.
My worry would be, once it ran out of salt it would just float to the surface, then you would have to refill it again reknot it. You can also by plastic line ties at homedepot, that might be able to remedy that, or somesort of small clip.