On Windows and GTK+ you can specify the mnemonics (underlined letters) in a button panel with the
:mnemonics
initarg, for example:
(contain
(make-instance 'push-button-panel
:items '(one two three many)
:mnemonics '(#\O #\T #\E :none)
:print-function 'string-capitalize))
Notice that the value
:none
removes the mnemonic.