Hiding Ribbon button based on the process stage

USIING CRM 2015

I have changed out of the box Process  for "Lead to Opportunity" to be something like this

Propose > Evaluation > Close

I want the out of the box "Qualify" and "Disqualify" button to be only visible in the Evaluation stage.

Could you kindly tell me  - what would be the easiest way (code\configuration) to achieve this?

Thanks,

Hasib

Hasibur Rahman