Aperture setting when vidoeing with 60D

Does anyone know if/how I can set the aperture on my 60D while I am using video mode? I have it set for no auto focus and manual zoom. However, at these settings, there does not appear to be someplace for me to set the aperture.

I have read the manual over and over and it does not address this issue (at least that I can find.)

Thanks for you assistance,

Harold