Y.S.
A diaper at naptime and nighttime ONLY is ok. Every other time it needs to be cloth trainers or underwear. I don't know if you can do it in 3 days but for sure as long as you stick to a routine you can do it.
Remind him every 1 hour or so to go to the bathroom. Take him w/ you when you go pee. Limit liquids and hour or two before bedtime. When going out take lots of clothing just in case of accidents.