I would probably phone the stake holder and tell that person your concerns and explain why you have the concern - for example - what is the risk of that stake holder not attending or providing support, etc.  Ensure they understand what their role is, how important it is and what impact he/she can have on your project.  If his absence will delay the project and ultimately cost him/her money then set that expectation early.   It will also help you to understand what is going on in his/her life that causes him/her to postpone meetings - is it because you schedule a meeting at 9:00 in your time zone which really equates to 7:00 a.m. in his/her time zone and he/she is the caregiver for his/her children and therefore can't always make it? ( as an example). 

A phone call would be my advice as a first step.  Set expectations.  Be sure his/her role is understood.  Understand their position and accommodate as much as you can.

Good luck!