Exchange EWS PushSubscriptionRequest 2010: How to to get notified using a service account that has permission over some users

I am able to subscribe to my account's contacts using "my" credentials and get notified

on changes to contacts by EWS.

For an application with thousands of users, creating subscription requests using each user’s

credentials is not workable.

So  I have created a service account (sa@business.com)  that has full permission

over my mailbox (my@business.com).

I am able to subscribe to my service account's contact  using "service account's credentials

and get notified on changes by EWS.

Now I just have one subscription to the service account.