No, you can't do that. You would need to use the radial menu if you want to target other allies. However some spells, particularly party spells (healing, status cure, etc.) can be upgraded to a "+" version that applies the effect to all party members - at the same cost as the single target variants. So this kind of mitigates the need to target a specific ally with the shortcut anyway. Alternative you can just switch to the ally you want to apply it to and use the shortcut. Although with the delay in character switching during battle, this isn't going to be any quicker than just using the menu.