Paint Polygons: You can resize the brush, so you could paint like half your model in no time at all. Selecting through an object: Goto Window: Settings/Preferences: Preferences... From there click on the Polygons category. Then find "Backface Culling" and turn it on. This will avoid selecting (and viewing) polygons that have their normal pointing away from the camera. Keep in mind, this means if you had a sphere, delete one face...it will look as though there is nothing on the other side, when in fact there is (the normal on the other side of the geometry is facing away from the camera, so it will not show up). Also, I have to restart maya after changing this option for it to take affect (not sure why). Toggle Select: Control and drag click always subtracts from selection. Control + shift click always adds to selection. And as you know, Shift click toggles selection. Not sure what else to say. The boolean idea I think would work, but I can't get booleans to do what they are supposed to on my computer right now. But if you had extra geometry, you could again just use paint selection and delete it.