Just an update to this, didn't need o2 sensor blanks in the end as dynojet would have done it manually with a resistor when they were fitting the PCFC.
Turns out that the blanks I bought didn't work, nor did the resistors dynojet tried to fit. Turns out that my bike is an oddity and they had to send away the ECU for a few days to disable the o2 sensors properly (no extra charge for this btw). they have (or someone they know) have done a 2019 before and the sensor blanks worked, so no idea why my bike was different.
Top marks to dynojet by the way, they were not happy until everything was sorted for me and didn't cost me any extra cash! (£216 for purchase and fitting of PCFC, £230 for the dyno run and custom settings).