Well, you could create a set of dummy abilities with no icons and just shortcuts for your hotkeys, and use triggers to order the unit. You could also use the "Game - Force UI key" instead of ordering unit, but i don't know the codes for numPad keys (and it wouldn't work if someone has custom inventory shortcuts)
And for your other keys: A is default for attack, so unless the unit has no attack, the shortcut won't work.