Why not take one of your current blazers to the tailor and ask them to add an inner pocket? I'd try this with a less loved item for the first round or two. You can also try out a vertical or horizontal pocket placement. Depending on how fitted your blazers are and how heavy you intend to load that pocket, it might look better to add the pocket lower on the body than a traditional men's inside chest pocket placement. You could also add pockets on both sides to help balance them out when you carrier heavier items (smartphone, etc) or it might hang a bit crooked.

How to tutorials
http://applefanatic.org/ipod/sewing-...et-t43196.html
http://ths.gardenweb.com/forums/load...233419026.html
http://www.craftsy.com/article/sewing-welt-pockets
http://www.fashionsewingblog.com/sew...-welt-pockets/