Office 365 proplus C2R updates saturating our Internet Line

It's possible but it might take some heavy lifting. It would probably require changing how Office 365 ProPlus is deployed and managed. 

Microsoft calls this the Locally Managed scenario in their best practices, which "uses on-premises file distribution systems to deploy <and update> Office 365 ProPlus".  The gist of this would be to have a file share with the downloaded Office updates, using the Office Deployment Tool (ODT), then using this same tool to tell clients to download updates from this location.:

The benefits are the update should only be downloaded once across the internet connection (assuming all clients have good access to the file share).  The downside is it takes more work.  There are other options like Configuration Manager, which has the ability to manage updates. 

Lots of details here:

https://support.office.com/en-gb/article/Best-practices-Locally-managed-scenario-48c953de-270e-4809-bd7d-93431159a047

https://blogs.technet.microsoft.com/office_resource_kit/2014/01/28/managing-updates-for-office-365-proplus-part-2/

https://support.office.com/en-gb/article/Choose-how-to-manage-updates-to-Office-365-ProPlus-e486afce-ad31-4889-87a4-28796751bb86

https://support.office.com/en-gb/article/Configure-update-settings-for-Office-365-ProPlus-a073ea21-62ed-40ef-8405-fd287f7d0b11