I did figure out a way to use it, It's rather simple when put into the right words. Here's the steps. This should work with any Hex Editor, but I used Cheat Engine.
1. Get a Hex Editor, like Cheat Engine.
2. Run DF, get to the embark world screen.
3. Run Cheat Engine, Select the DF process from the process select button at the top.
4. Go back to DF, find the location that you want to embark to that you normally can't.
5. Now, Read Closely. Go back to Cheat Engine, and find the "Value Type" menu, click it, and go to Array of Bytes.
6. Check "Also Scan Read-Only Memory"
7. Now, near the top, where it says Hex, enter this value - 66 83 7F 1A FF
8. Press First Scan.
9. Let the scan finish, and an address should appear to the left highlighted in Green.
10. Right click it, and select "Disassemble this Memory Region"
11. Now, right Click the Value that is below the one that is highlighted. The value you must click should have 74 04 under the Bytes, and the Opcode should start with je. Right Click it.
12. Another more advanced menu should pop up, select "Replace with code that does Nothing"
13. Press okay, and if you did it right, a few lines opcode should turn into nop.
14. Go back to DF. Embark anywhere you want - Castles, Mountains, even oceans if you want to have some instant fun.
Enjoy!
And I tried that new Just Embark tool, got some errors, didn't work. I would recommend trying it first, but if it doesn't work, try this method.