So with thanks for Humper, Phil, some dude called Nick Moxley and a file, I've now replaced the stock fanatec damper with a mugen one.
I originally found out about the mod via the Inside Sim Racing forums where Nick has detailed how he did the mod. I then found he was a member of the same Sim Racers facebook group as me so I was able to message him and get further details.
I remember Phil had these pedals and had mentioned modding them; he had the mugen damper which were bought in a pair and when he sold his pedals to Humper he also sent the spare damper.
Humper still had the spare and was happy to sell it to me. Don't you love it when a plan comes together! Looking forward to trying it out later.