Hugh, it’s a pity that you are not going to improve on this. The idea is excellent. So simple. I’m not able to decide how easy it would be to circumvent it automatically, but I really think you should give it another try.
I think that odjinud had the same problem I had. I, too, thought it broke on my iPhone, until I read some other jQuery-documentation telling to use the fall back mode:
1) click on the icon.
2) clik on the empty box.
I was mistakenly trying to drag’n’drop, which apparently doesn’t work. This – off course – has to be clear to the tablet user.
I suggest you make an instructions field for tablet and one for desktops. Or something similar. Otherwise we will loose too many users.