I am looking to retard the ignition timing by approx 1-2 degrees on my carbed R1 motor.

Is fitting an adjustable ignition advancer the only way to do this?

Assuming this is in preparation for your turbo conversion according to holeshot racing you don't need to retard the ignition if your running sensible boost and decent fuel!
mines been fine for the last two years running 12psi.

My thinking was the same to the extent i imported a Graves adjustable advancer from the states (think ive still got it somewhere if you still want one)