Unfortunately Option 61 is something the R1 doesn't support. It can be changed on the NETGEAR Nighthawk Pro Gaming routers because they have a NETGEAR specific section of the interface with more complicated controls. You might need to use your Sky hardware and connect your R1 to that. I'm sorry that I couldn't be more helpful.
I don't know if Sky can release this limitation from their end, or if they really just hate people trying to use their own hardware in their own homes.