Full Mailbox Permission for Group members

In my environment I am using Exchange 2010, & I need to provide a service account which will have full permissions to create, update, and delete items for exchange mailbox for those users who are a member of a group. Meaning that service account will have full permission for those users who are member of a specific group, please advise which power shell command I can use to do so.

Service Account>Full mailbox permission on group members>ultimately full permission of the member of the group

So far I have found the following in the below URL:

http://social.technet.microsoft.com/Forums/exchange/en-US/9840fd13-daf8-45aa-ab35-4a827f1ba1e0/exchange-2010-unable-to-assign-full-access-permissions-using-a-security-group?forum=exchangesvrgenerallegacy


“If you only want members (in this security group) to have full access permission on the mailbox, you can use this command to achieve the goal:
 
Get-DistributionGroupMember “Test Group” | foreach-Object { Add-MailboxPermission “Usermailbox” –AccessRights FullAccess –user $_.Name}
 
Not sure does the power shell command will be applicable for my above requirement, as because if I follow the above power shell command in this case group member will have full mailbox permission to a mailbox but my requirement is opposite, i.e service account will have full mailbox permission to group members, can you please advise.