Namaste!
I'd like to share a link with you:
http://www.veoh.com/users/sammydacatThere are two videos there that my teacher made specifically related to cleansing/charging/programming crystals with Reiki.
Yes, it's definitely possible. Reiki/chi/universal energy flows through all things, whether they be sentient beings or inanimate objects. There's no point in my repeating the process to do these things here because the videos I mentioned explain it quite thoroughly. A couple of points though:
I generally don't advise programming crystals. The interesting thing about crystals is that they all have their own unique vibrations, or "tone" to their energy. It's best to work with their natural energy (so don't program a random crystal to soothe a headache, but grab some amethyst or such instead). You can however program any crystal with an intent for healing, to ensure the energies only work for the highest good and remain pure. If you need a crystal with a very specific intent and don't have any that suit the job, then completely clear/cleanse a simple quartz crystal and program that.
An interesting theory my teacher presented was that you could make use of HSZSN to continuously channel Reiki through a crystal, thereby perpetually charging it (and keeping it cleansed, although you may want to continue cleansing by other methods periodically).
