Hi George. Congratulations on a succesful NPS programme, I would assume that many companies would be very happy getting just a bit of same success. Tying NPS to incentives, KPIs (leading to incentives) or similar, can in many cases lead to the wrong behaviour, if you start attracting focus on personal reward rather than the sucess and purpose (for the company) of driving a good customer dialouge.
Secondly, most companies would usally tie the NPS to incentives and KPIs to get tracktion, which you already have. I would say that the challenge is to keep momentum internally, grab the individual good customer stories that made a difference for your business and communicate it. If your NPS lead to increased business or financial performance, the client managers will assumingly be incentivized through those metrics anyway.
Good luck.