The new Blast Thru Editor adds support for modifying the scores in the highscore table. This means it is now able to calculate the score checksum the game uses to find out if someone cheated by editing the bt.ini manually.
The algorithm for that is actually pretty damn easy, don't ask me why we didn't find this out earlier:
Add each (score % 256) together. That's it.
Download the new editor in the download section. Have fun!