This item- https://www.amazon.co.uk/92cm-430cm-Drilling-Extendable-Stainless-Telescopi...
I used it temporarily to hang curtains over 400cm windows and it worked great. Divided into parts and there are online instructions to reconnect.
Extra long/ adjustable tension curtain rod (Chalk Farm NW3)
This offer has been gifted to someone and is no longer available.