It might be difficult. A cat used to going outside is living a far more natural and wonderful life and may suffer from the sudden decrease in activity and stimulation. You can help him by playing with him and keeping him involved in the stalking/thinking games he played outside. Cats, I find, are much more active and energetic than many people think.
You may have some trouble getting him to be active during the day and not at night. Again, playing with him during the day will help with that. Tire him out in the day. LOL, how long can you drag a string around your house for him to chase?
An option you might consider is building him a secure outside cat run.