Update plugins for other than site admin

Hi there,

I have build a website for my client, I'm the site admin and I've created a custom user role for him.

I want him to be able to update all plugins when needed. He get's an error when trying to update the WPMU plugins. Other plugins are fine.

Is there some custom user capability I have to grant his user role to enable him to also update WPMU plugins?

Please let me know what to do.

Kind regards,
Steven