How to display hint for a disabled control?

There is a simple solution: place an empty TLabel over the checkbox and set its Hint to the value for the disabled checkbox state. The label has to be AutoSize off and you can enforce position and size by its BoundsRect property set to that of the CheckBox.

When the CheckBox is enabled the Hint of the Checkbox is used, while the Hint of the Label is used when the CheckBox is disabled.

Update: just saw that Bummi mentions a similar idea in his comment.

The official answer: you can’t.

The workaround: you could try using the form's MouseMove-event (assuming that won’t be disabled, of course), and if the mouse cursor is over the relevant control, display the appropriate hint.