Lori,
The Tumil-K comes in tablet form and in paste form. I would stay away from the paste kind, because most supplements are put into a paste to make them taste better. And the way to make most of them taste better is to add something sweet to them. If you look at a paste style supplement of any kind, read the ingredients before buying to make sure there isn't sugar or some other sweetener in them.
The tablets can be crushed and made into a powder that you can hide in his food. I am not sure what the dose should be. When I tried to buy Tumil-K, I found it online, but the sites said I needed a prescription to buy it. So you'll probably need one too, and your vet will know what dose Copper will need. You'll just be able to buy it cheaper if you buy it online rather than from the vet.
Bob's potassium was mainly delivered by way of sub-q fluids. He had to have those anyway at the beginning of his dance, and the vet just added potassium to the bag so I could do two things with one method. Even after he no longer needed the fluids to keep him hydrated, she had me continue doing the potassium that way.
I think "normal" runs from 3.3 to 5.5 on potassium levels. I've seen different ranges though, so the 3.3 might be considered "lower than normal" by some people. Bob ran in the 3.0 to 3.5 range most of the time.
Here's an example of "normal" I found:
http://www.felinecrf.com/tests0.htm
Approximate Normal Ranges for Common Tested Blood Values
BUN 14 - 36 MG/DL
Creatinine .6 - 2.4 MG/DL
Calcium (Ca) 8.2 - 10.8 MG/DL
Phosphorus (P) 2.4 - 8.2 MG/DL
Potassium (K) 3.4 - 5.6 MEQ/L
Sodium (Na) 145 - 158 MEQ/L
Packed Cell Volume (PCV) 29% - 48%
Carl