This is obviously against policy, and although what he is doing doesn't require to do any interaction with anyone in the office it's still wrong
Change the policy slightly
I think you should change the work from home policy for your team to be at your manager's discretion, meaning at your discretion. This way you can say they are following the rules, and this person is working from home more because they are such a good contributor.
Don't make the mistake of attempting to force the developer to come in just for the sake of init. If they are productive leave them alone, punishing them may tick them off and they may leave. Are your prepared for that possibility?
Note: Based on what I could glean from your post, I assumed you are this person's manager. If you are not, then report the behavior to his manager and see how they want to proceed. I still think in this case I would leave the developer alone.