Para clicar usando as teclas para mouse explica em detalhes como MouseKeys funciona:
To click, press 5 on your numeric keypad.
To double-click, press + on your numeric keypad.
To right-click, press - on your numeric keypad, and then press 5 to click, or press + to double-click.
To click as if you were using both mouse buttons at once, press * on your numeric keypad, and then press 5 to click, or press + to double-click.
To switch back to standard clicking, press / on your numeric keypad.
(formatação e ênfase minha)
É da documentação do Windows XP Professional, mas ainda se aplica.