Find out what God is teaching them. You can tell them what you have observed in each of these areas. If you are a reader, write and then send short book reviews of each of the books that you finish. Offer to send them the book if they are interested in reading it themselves. Send reading material, magazine subscriptions, news clippings, the church bulletin.
Missionaries can vote by absentee ballot.
You could offer to send them any forms they need. If they are interested, send them brochures or newspaper clippings which explain stances on important issues. Send them clippings about their country or ministry. It shows that you are thinking about them. It also communicates that they are not alone.