There are a couple of ways to thin it. I'm not familiar with the plane you're talking about so I don't know how you would accomplish pouring thinned epoxy and getting it to stay where you put it...but- I guess I'll let you handle that part.
The first way is to mix the two part epoxy thouroughly, as usual. Mix it in an unwaxed paper or plastic cup. Add a little denatured alcohol into the cup and stir thouroughly. Keep adding alcohol until the consistancy is where you want it. Do not try to add the two parts of the epoxy in the alcohol independently. It must be mixed first, then the alcohol is added last.
The second way is to heat the epoxy. Again, mix first then heat. You can use a heat gun or heat it very, very carefully in the microwave. Needless to say, you could ruin a microwave this way if you're not careful.
For both of these procedures, slow drying epoxy is superior to 5 minute epoxy. Also, thinning epoxy increases the drying time drastically but the strength is unaffected as far as I've been able to tell. Don't be alarmed if it stays tacky for several days. If you've mixed it properly, it will dry eventually.