To become creative on command, create productivity triggers for yourself. Use the same tools, sit at the same desk, listen to the same music. Do this long enough and your brain will start to associate these things with productivity. For example, Stephen King has a little writing routine:
There are certain things I do if I sit down to write. I have a glass of water or a cup of tea. There’s a certain time I sit down, from 8:00 to 8:30, somewhere within that half hour every morning. I have my vitamin pill and my music, sit in the same seat, and the papers are all arranged in the same places. The cumulative purpose of doing these things the same way every day seems to be a way of saying to the mind, you’re going to be dreaming soon.