I agree that it's better not to use an app, since you don't want to be dependent on a specific voice to get you going, among other things.

The technique you describe (which I also use) is explained more fully by Roger Wells in "Happy to Burn"[1] which I found out about from the "Mind Perfomance Hacks" book[2] originally.

[1] http://www.sankhara.com.au/shop/products/detailFree.html?Pro...

[2] http://www.worldcat.org/title/mind-performance-hacks/oclc/64...