I hate being married to my cell phone - but it is handy to have at times - this is what I did - get a "Lifeproof" case and floater and use a small bungie cord with terminal connectors crimped on each end and mount it on hood as shown.
http://www.lifeproof.com/shop/us_en/iphone-5/nuud/
Kelly
http://www.lifeproof.com/shop/us_en/iphone-5/nuud/
Kelly