Usage of the -I flag of bash's complete command

Question

I want bash to autocomplete cod<TAB> to codium (discarding other commands that might also start with cod)

Looking at the manual of the complete command, I found the -I flag which seems to be what I need.

I ended up with the following solution:

complete -I -F _command_completions -o bashdefault

function _command_completions() {
  # cod<tab> completes to codium
  [[ $2 == cod* ]] && COMPREPLY="codium"
}

which works, but I was wondering: Is there a more succinct way of achieving the same result?

For example, something like:

complete -I -W 'codium' cod

this causes the words: empty string, c, co, cod, codi, and codiu to complete to codium which is not what I want.