Was reading through the above posts re: food ... Lucy, if you can't transition him out of eating kibble, please at least transition him from the Purina D/M dry to either of the two dry foods others have recommended (Evo or Young Again, I believe.) Because the D/M dry is @ 31% carbs, & you say he's eating about 3/4 cup of the D/M per day, right? (One of your earlier posts:
He eats Fancy Feast or Friskie's pate' and ProPlan DM. I can only get him to eat about 1/2 can per day, 1/4 for breakfast and 1/4 for dinner. He much prefers the dry, and he gets that throughout the day, about 3/4 of a cup all told.)
Lucy, that amount of high-carb dry every day is really shooting you & Squallie in the foot. I'm feeling fairly certain that this is playing a significant role in his numbers not coming down as much as you'd like: Squallie's getting a dry food that's
3 times the max. amount of carb content that a diabetic cat should be consuming. (Not beating you up here, just encouraging you. It took me a while to wrap my head around all of this the first time around with Bat-Bat, too.

)
So if you must feed him dry at those times he refuses to eat any brand of low-carb canned,
please transition him from the D/M kibble to a much lower-carb kibble. (Any extra cost will be cancelled out by less need for insulin over time.) Make that transition bit-by-bit, though - Ex: 75% DM/25% Young Again or Evo; then 50/50, then 25/75, etc., making sure you keep monitoring because his BG numbers will likely drop considerably (and his dosage of insulin will likely have to be reduced then, too).
Keep on keepin' on, Lucy ... Squallie will get there, I know: because I can see (even from this far away) how much you adore your kitty!