Premiere Pro has never had this ability.
Thank you for answer.
I know Premiere Pro 1 and 2 didn't had this ability, but I thought maybe since CS 5.5 has improvements in custom keys and maybe elsewhere, maybe they have added this too.
It could be useful for example taking a command buried deep down in some menu, but you are using all the time that command - and you could bring that in front, on a toolbar.
So I guess I will ask this again for Premiere Pro CS 7
I just use the keyboard shortcuts myself.