I know the text book answer is no , but if i take methadone in the early morning & take ritalin (methylphenidate) in the afternoon (not long term) , would ritalin (methylphenidate) work?

May be: In theory the two drugs don't interact, as they have opposite effects, not additive effects, methadone has a long half-life, it stays in the system longer, at least 16 hours, its elimination depends on many factors, how active is the liver, how acidic is the urine for example or alkaline, etc.. Also depends on other medicines you are on, counsel your doctor again, both are schedule II medications,