How do you taper dopamine agonists for RLS in patients experiencing augmentation?

Slowly. Abrupt withdrawal from agonists can cause mood dysregulation (dopamine agonist withdrawal syndrome) and in RLS patients, would likely exacerbate RLS symptoms.

Adding gabapentin to the regimen prior to slow withdrawal of the agonist would probably help avoid worsening RLS symptoms during this ...

It depends upon the severity of symptoms and what the future plan is.

If someone is having an otherwise good response but needs higher doses to maintain that effect, I typically start them on the new medication first to establish tolerability and initial efficacy, then cut the dopamine agonist dose ...