Emacs: Disable shift-selection in CUA-mode

I managed to disable the built-in shift-selection via (set-variable 'shift-select-mode nil). And I like the C-Ret-column-selection of CUA-mode. But CUA automatically enables shift-selection (but seemingly not via the variable shift-select-mode).

• So, is there a possibility to disable shift-selection within CUA-mode?
• Or: Is there a way to use the column-selection-feature of CUA-mode exclusively, i.e. without any other CUA-things?

This isn't a solution, but FYI...

I noticed this variable mentioned in the help for cua-mode

cua-highlight-region-shift-only is a variable defined in `cua-base.el'.

*If non-nil, only highlight region if marked with S-<move>.
When this is non-nil, CUA toggles `transient-mark-mode' on when the region
is marked using shifted movement keys, and off when the mark is cleared.
But when the mark was set using M-x cua-set-mark, Transient Mark mode
is not turned on.

cua-mode does this:

(setq shift-select-mode nil)
(setq transient-mark-mode (and cua-mode
               (if cua-highlight-region-shift-only
                   (not cua--explicit-region-start)
                 t))))