I have used this technique successfully for five years. At the end of the season they are in my largest pots and are mahussive. When I have cropped the last fruit I follow these steps:
1. Chop off every branch back to the stem
2. Chop the stem off at about 10cm (see first post of this thread)
3. Remove from big pot and shake off all the old compost
4. Wash off the remaining compost in lukewarm water
5. Trim the rootball with scissors so that it will fit nicely in a smaller pot (use the smaller pot as a size guide and remember that we nee to put soil in too)
6. Put fresh compost in the bottom of the new (smaller) pot.
7. Sit the trimmed down plant onto the compost and pack fresh compost all around (press it down cos we need to get it between the roots BE CAREFUL AND TRY NOT TO DAMAGE THE ROOTS)
8. Store somewhere at room temperature with lower light levels (ie. not a window sill... but not pitch black 24/7 either)
9. In February get them on a warm window sill and they'll bounce back
This method doesn't work for everyone but has never failed me.