I've been doing my cat's blood glucose testing for over a year, and I'll still not get enough blood (or even no blood at at all!) if I fail to warm the ear first. It makes a huge difference! I use a sock filled with rice, but a baggie filled with warm water would probably work better than a pill bottle since the baggie will form to the area. Just be sure to test the temperature on yourself so you don't burn your kitty. Take your time to thoroughly warm the ear.
You can also apply a very small amount of plain petroleum jelly to the ear before testing. This helps promote healing and it helps the blood form into a nice bead for you to collect with the testing strip. Emphasis on just a little, you don't want a super greasy ear.
Try not to poke the exact same spot each time.
I fold a piece of toilet paper into thirds and place it behind his ear. Making sure the skin is taught by sandwiching it firmly (firmly, but not painfully firm!) between the lancing device and the toilet paper makes for a good poke.
I used a few different lancing devices and lancets and found the Accu-Chek Softclix was the least painful to use. Your kitty may be more cooperative if you try this lancing device.
Teaching your cat to come and sit on a special mat or pillow can be helpful as well. If you need him at a better angle, you can just spin the pillow around instead of trying to get him to move exactly how you want. I'm reading a cat training book titled "Naughty No More!" by Marilyn Krieger and one of the first activities is training your cat to come to a specific spot.
After a poke, even if it's unsuccessful, be sure to lavish him with reward! You want this testing experience to be followed by a clear reward to form a positive association, otherwise he has no reason to cooperate.
In the beginning, I would not poke my cat's ear more than 3 times in one attempt. I would space my attempts half an hour apart and switch ears between attempts.