have him watch this video series on youtube (you should watch them too)
How to Snowboard: Step 2 - Skating and Stepping - YouTube
then just make him do that stuff
write down each step in a little notebook or save the vids on your cell phone to remind you not to skip steps
i did this with my gf it worked pretty well, we did the first few videos then she took a lesson and i helped her finish the videos and what they taught her in the lesson.
but lessons really aren't that expensive especially if you can get him a package like the learner lift ticket and lesson and rental together