Open all selected files as hidden buffer?

Is there a way Ctrl-P can open all selected files as hidden buffer? This is how I tried to load files into my buffer:

<c-p>               (opens Ctrl-P in file mode)
<c-o>               
a                   (marks all files in the match window)
i

The last "i" was intended to open the selected files as hidden buffers. Instead "i" appeared in the search dialog.

From :help CtrlP

Opening multiple files:

  <c-z>
    - Mark/unmark a file to be opened with <c-o>.
    - Mark/unmark a file to create a new file in its directory using <c-y>.

  <c-o>
    - Open files marked by <c-z>.
    - When no file has been marked by <c-z>, open a console dialog with the
      following options:

      Open the selected file:
        t - in a tab page.
        v - in a vertical split.
        h - in a horizontal split.
        r - in the current window.
        i - as a hidden buffer.
        x - (optional) with the function defined in |g:ctrlp_open_func|.

      Other options (not shown):
        a - mark all files in the match window.
        d - change CtrlP's local working directory to the selected file's
            directory and switch to find file mode.

Here is how to open all selected files as hidden buffer.

Add this line to vimrc:

let g:ctrlp_open_multiple_files = 'ij'

where

i - all files as hidden buffers.
j - after opening, jump to the first opened tab or window.

In Vim:

<c-p>               open Ctrl-P in file mode
<c-o>               open a console dialog
a                   mark all files in the match window
<c-z>               mark/unmark a file
<c-o>               open marked files as hidden buffers