I'v all ways cut this back whenever it looks like its going to be in my way, it is proberley not the right answer but has worked for me, never tried to strike cutting from it though. I'd leave the berries as long as I could as the birds like them. So if your only nipping off a little it will not make much difference.

We have one trained against a wall - the advice we found was to cut back the non-berried shoots at this time of year, which exposes the berries.

I also understand that these shoots can be used as cuttings - so why not give it a go? Try some in a trench lined with sand, and some round the edge of a pot.