Financial Penalty for Unresponsive Customers during Onboarding

Hi all,

First time poster here; looking for some GGR community wisdom.

We are a SaaS startup with a relatively complex product.  Our implementations are fixed-price, high-touch, last 4-6 months, and require a 2 hour/week customer commitment throughout onboarding.  

While most of our customers are very responsive and eager to go-live, we have one that is not.  They are often late, miss meetings, struggle to complete required tasks, and lack a shared vision or strong leadership.  Because of this, their project is delayed and requires significantly more of our team's time than normal.

We've tried to work collaboratively to get them back on track with no luck.  At this point, we need to amend their contract to incentivize the necessary change.  The (now realized) risk of significant project delay wasn't a strong enough incentive.  So, we are exploring how to amend their contract to include financial consequences if there is a continued lack of cooperation.

A few questions:

• Has anyone done this successfully?  
• If so, how did you model the financial penalties? Percentage of implementation cost? Cost per delay incident?
  
• Any other advice?

Thanks for your help!