Jay obviously you need to teach them manners when eating. Mine are trained to take a bite and pass the cube to the next in line. .
Since you have a couple of pigs though maybe try cutting the cubes into additional pieces with a razor... 2 cubes to 4 cubes. The smaller cubes will stick better.
You can also try taking the cube and submerging it hold it in the water a minute or so then press to glass. The extra time wet will allow it to smush a bit better.
Lastly.. switch to looseand drop into the filter out flow.
Hth,al