On the shut off valve there should be a small "Cap" on the side of the valve, that is what it is for.  You remove the cap and simply tape it to the pipe, you may (Depending on which way the line slopes) need a cup or bucket under the valve to catch drips. 
Option 2 is a device called a Saddle T,, You get one (These are used for things like adding an ice maker) drill a hole (The instructions with the "T" say what size) in the pipe "Downstream" of the valve, install the saddle and saddle T. Then open the T valve to let air in and close it when you restore pressure. 
http://www.naturalhandyman.com/iip/infxtra/infsad.htmlClick the link for more info on Saddle T's.. Including install instructions and a photo of one.