Hi Maltey, welcome to the forum! I am not sure but I think fruit sugars are just as bad as ordinary sugars for diabetics - I would check before you make any. The very sweet tooth could well be a symptom of diabetes and you may find that this eases off for him once he gets his blood sugars under control. It would be best if he could reduce his reliance on sweet things because as you say lots of artificial sweetener can have a laxative effect. I have heard good things about stevia, which is a new sweetener which is made from a South American leaf and therefore a bit more natural than other artificial sweeteners - I haven't tried it yet - because I still have some Splenda yet, but I have found Splenda makes my blood glucose spike so I might just throw it away anyway.
I made some low carb chocolate muffins yesterday - you can find the recipe under the 'chocolate paradise' thread on here. They were wonderful. Also Boots sell Strawberries and Cream and Caramel sweets in their diabetic range, but go easy ...