I almost use the same technique, but instead of making a bit of starter wort to fill up the bottle I simply open up a small box of apple juice (20 cl) and pour that in the bottle. I give it a good swirl, put a balloon over the "neck" and set it on top of my set top box (which is always in de low 30°C).
In most cases the balloon will be erected after 24~36 hours and I will pour it into an erlenmeyer with starter wort and put it on the stirr plate.
Never had a failure except for one time I was growing bacteria instead of yeast (it smelled like the worst cheese you can imagine!).
Niels