Here are a few thoughts on how to fill gelcaps with a diluted essential oil mixture. The essence can be mixed with any vegetable oil; wheat germ oil is a good choice because it's high Vitamin E content also makes it a good preservative. You can fill the caps with the just the oil mixture, but this can be tricky and the caps often leak. A better way is to first dilute the essence in a small amount of vegetable oil or glycerin (1 - 2 parts oil/glycerin to 1 part essence), then combine the mixture with a food - grade dessicant such as cornstarch or Bentonite for internal use or a combination of both. The capsules are now easily filled with the dry powder (you can use a capsule machine* to produce a large number of caps quickly). The amount of absorbant is calculated so as to end up with the desired amount of essence, usually 1 -3 drop(s) per capsule.
An excellent source of information on this subject is the book Medical Aromatherapy by Dr. Kurt Schnaubelt.