I installed the Toodledo App on my Ipad yesterday and had the same unpleasant discovery. I understand that you have a lot of things on your roadmap, but for what it's worth, I believe you should increase priority on it.
Seems that this feature is still not available. I have switched from RTM over to Toodledo and have upgraded to a paid account. Whilst on the Web Interface, I can work nicely shifting tasks and turn them into subtasks, something I'd like to do on my Ipad, please implement this on the Ipad platform asap.