Tricks but no treats

I have a four-year old-Cavalier King Charles Spaniel called Alfie. As a pup I took him to dog training classes using treats as a reward, which proved beneficial as he became my perfect dog, well trained and obedient.
Throughout the next few years now and again he would need reminding of particular things like walking nicely on a lead, no barking when getting ready to go out and the stay command when you walk away. Which we did again using treats like in his training classes which once again proved successful.
However in March this year Alfie was diagnosed with diabetes and is now on a strict eating plan, which includes NO TREATS due to his blood sugar levels and insulin. Recently his inappropriate behaviour has returned regarding the same things as before as well as barking at the yappy dogs next door in the garden. This time we are unable to reward good behaviour with treats so we have tried a variety of toys but he isn't interested in them and praise doesn't seem enough as he isn't responding.
I have searched the web but to no success as each time it is advised to use treats or toys as a reward with no further advice for people with dogs in our situation.
Any advice would be gratefully received as we wish to help Alfie by correcting this behaviour now before it gets too out of control.
Miss Louise Hawkins, by email

I would have thought that the answer for Alfie would be clicker training. I was very involved with obedience training with my border collies until I qualified as a vet when I found that I no longer had spare time on my hands thanks to on-call and long working hours. Unfortunately, having qualified in 1989, clicker training was after my time so I have no practical experience of it, but it is certainly training without treats which is what a diabetic dog needs.
Alison Logan, vet