Metformin: splitting a.m. pill?

I currently take 2000 mg. of metformin daily, 1000 - a.m. and p.m. Now that it's summer, I am more likely having sandwiches at lunch and primarily vegetables for carbs for evening meal. I'm not exactly sure how metformin works, but would it be advantageous to split my a.m. dosage between breakfast and lunch when I know I'll be having a higher carb meal? I currently have no problems with blood sugar in late afternoon or evening, but fasting numbers are still varying between 98 and 138, so I don't want to mess with the evening dosage. I don't see doc until Sept. or I would ask him. I have regular metformin, not the extended release.