Since it bugs me to no end to search for threads like this and the OP doesn't post an update or wrap-up, I'll make this a two-part ending since I'm waiting 24 hours for the paint to harden on my adapter.
What I started with...a piece of bar stock mild carbon steel that's (somewhat) easily bendable. Available at any hardware store for around $5.
After measuring, bending, drilling, filing and painting, here's what I came up with:
Will post a final pic on the bike after the paint has properly cured. This piece is pretty strong too...I'll certainly worry more about the Technium imploding than I will the rack coming loose.