You need to create an additional AG to group servers together into a single cohesive unit for management.
Solution
Using a graphical user interface via ESM
Launch the Exchange System Manager (Exchange System Manager.msc).
If you don't see an Administrative Groups node in ESM's lefthand tree pane, see Recipe 2.17.
Right-click the Administrative Groups container and choose New Administrative Group.
Open ADSI Edit (adsiedit.msc) from the Windows Support Tools.
Expand the configuration container. Drill down to the appropriate CN=<orgName>, CN=MicrosoftExchange, CN=Services,CN=Configuration, DC=<domain>,DC=<tld> container for your Exchange organization.
Right-click the CN=Administrative Groups container and choose New Object.
Type the name you want to assign to the AG in the Value text field. Click Next, then click Finish.
Discussion
AGs are used to define boundaries of administration, usually in organizations where administrative responsibilities are decentralized. For example, many companies choose to create separate AGs for each geographical region, and then they delegate administrative control over those AGs to administrators in that region. This provides a flexible way to keep all of the European servers in one group and all of the North American ones in another; it's also common to see multiple AGs defined to match the structure of business units or divisions. Because servers and routing groups are both contained within AGs, you can group resources that should be managed by the same people together and delegate access to them.
Microsoft recommends against creating AGs from VBScript.