One of my parenting magazines had some suggestions for making a parent's temporary departure easier.
1. Count Down the Days- Make a tear-away calendar or something similar so they have something to help understand when the parent is coming home.
2. Look at the Lovely- Take along a stuffed animal or toy and photograph it doing cool things like flying or sightseeing.
3. Record your voice- Use the computer or smart phone to record a message, video, or story for bedtime.
4. Video Chat- Skype or gmail!
5. Start a Virtual Diary- familydetails.com has a free website for the family to write day to day activities, upload pictures and texts.
6. Create Together- If a parent is gone for a long time create a picture together. Start out with a single line on a page and mail it back and forth, adding one line or shape until you have a piece of art.
Here is an example of number 2
Mouse traveled with Daddy on his business trip.

Mouse went to the pool.

Mouse sleeps in.