It is also a remarkable experience to be there when your missionary is being set apart, right before they leave. Recording some of the statements made in a journal or blog, will be a special part of their missionary records that they can keep and share forever. It can be a source of inspiration to come.
Encourage your missionary to write in a journal and "enhance [his] ability to recall revelation". Share with him Elder Scott's take on obtaining revelation through recording.
Here is an excerpt:
"Revelation can also be given in a dream when there is an almost imperceptible transition from sleep to wakefulness. If you strive to capture the content immediately, you can record great detail, but otherwise it fades rapidly. Inspired communication in the night is generally accompanied by a sacred feeling for the entire experience. The Lord uses individuals for whom we have great respect to teach us truths in a dream because we trust them and will listen to their counsel. It is the Lord doing the teaching through the Holy Ghost. However, He may in a dream make it both easier to understand and more likely to touch our hearts by teaching us through someone we love and respect.
When it is for the Lord’s purposes, He can bring anything to our remembrance. That should not weaken our determination to record impressions of the Spirit. Inspiration carefully recorded shows God that His communications are sacred to us. Recording will also enhance our ability to recall revelation. Such recording of direction of the Spirit should be protected from loss or intrusion by others."