Den. nobile question

[Baz in Oz]

I have a large soft cane Den. that I believe is nobile. I bought it at a school fete a few years back and it hasn't flowered or set keikis.
Local growers tell me the thing to do with soft canes in this area is to put them outdoors on Mothers Day and bring them back into the shade house on Fathers Day and resume watering and feeding.
This is to get them to flower and not set keikis.
My problem is that the damn thing won't stop growing. It has two half grown new canes and another two just starting.
My other soft canes have dutifully set their terminal leaves and are telling to hang them in the pergola.
What do I do with this one?

Baz in Oz