I feed with the full bowl, normally thh hoard a little
Then eat it from the bowl, leaving what they don't like. I have had no problem with this, I normally fill it when I do the water if it needs it.
I give syrians honey sticks, carrot biscuits, babyfood,
Fresh veg, sunflower seeds, millet seeds and sprays.
You can get bitter apple spray, I don't know if this works, I have a bad cheewing boy, he now lives in a bin cage so he cant chew out, but putting a wood peg or weaving card where they chew can help.
Zoo plus and equaninecaninefeline are the sites I use
and eBay!
Hope this helps!