I had a day off today, and this problem bugged me until I did something about it. So here is a solution:

use Math::Fleximal;
print Math::Fleximal->new(
  "2dd9f2ba1f924996fa231fdceb4c6f57",
  [0..9, 'a'..'f']
)->change_flex([0..9,'a'..'z','A'..'Z'])->to_str();
[download]

which will print "+1owfX3qQrJC5h1IIWhMy23". Strip off the + and you are in business.

You will need Math::Fleximal of course.