gcm behind firewall

[Sven]

Hi,

I need to use gcm push notifications behind our companies firewall. In the documentation I can only find following note:

Note: If your organization has a firewall that restricts the traffic to
or from the Internet, you need to configure it to allow connectivity
with GCM in order for your Android devices to receive messages. The
ports to open are: 5228, 5229, and 5230. GCM typically only uses 5228,
but it sometimes uses 5229 and 5230. GCM doesn't provide specific IPs,
so you should allow your firewall to accept outgoing connections to all
IP addresses contained in the IP blocks listed in Google's ASN of 15169

Our IT-department cannot open the ports to the all of the 228 subnets of Googles AS.

Is there a workaround for situations like this? e.g. are there specific subnets for certain regions? or can I make any assumptions what ip-adresses are used by the gcm servers?

The app we are developing will be used quite often in scenarios like this, so it is not an option to use mobile communications instead of wifi.

I found several threads to this topic but couldn't find one with a satisfying answer.

Thanks,

Sven