By the way, this does work with views. So my suggested syntax fix above is correct.
Example:
Create a view mdl_user_fullname with two columns, the user id as id and a concat of the first and last names into a single column as fullname.
Then:
SELECT u.username, fn.fullname
FROM prefix_user_fullname fn
JOIN prefix_user u ON u.id = fn.id
%%FILTER_SEARCHTEXT:fn.fullname:~%%
works as expected. (Assuming your view has the same prefix_ as your standard tables.)