Thinking outside the Box!!
Firstly D/s is not simply about sex!
1, Always use all modes of communication available and that are practical to use e.g Skype, Email, Text,Phone Calls etc
2, Unfortunately you haven’t mentioned your subs Likes/Dislikes/Limits or his weaknesses and strengths.
3, Does he have a need for structure and discipline in his daily life? E.g when he gets up/goes to bed? Exercise regime, when he eats/what he eats, how he sleeps be it on a bed, a blanket on the floor, dog bed or in womens lingerie to performing a nightly ritual of thanks that you are his Master!
4, As you are a student you could easily set him a research task this can range from searching for the most informative websites to help with your course work to a hobby/interest that you require more information about…think outside the box!!!!!!!