Finally worked up the courage to try this. I must say that making the mold was probably the most entertaining part of the process, but the casting the resin was the most rewarding. I nearly destroyed the cast though -- as I demolded and started trimming the cast, I squished it on one side a little too hard and deformed it. Fortunately it wasn't fully cured, so I was able to bend it back. For the future, I'll make sure to wait an extra 10 minutes before demolding. Oops. ¯\_(ツ)_/¯
My thanks to the community for providing the techniques to do this, particularly Beetlecat for the instructional video.
PS: If you're in the Denver area, there's a place called Reynolds Advanced Materials that sells all of the Smooth-On products used to make the resin casts. They sell it for the same price as smooth-on.com, plus tax but minus shipping. It was really handy having this place to grab something quickly when I ran out of materials.