how to create invalid utf-8 characters in MySQL
Why not changing the text strings to a binary encoding or non-utf8 encoding, or to use binary strings (varbinary, blobs)? That will allow you to store all invalid values that you want.

Edit: To be more specific: change the type to varchar(255) charset binary, that may cause you all kind of charset problems .

@RLF, funny that you mention Wikipedia, text on the wikipedia is stored in binary format!