Good luck. I currently have a PER request in with Cisco for this feature. PERS Request ID# 8283. It should be the easiest thing in the world, but they haven't done it yet.
One thing I have noticed with running T1 WIC CSU/DSU back to back is that the links can run too "hot" with a short cable you might need to knock down the db level on both ends of the T-1 with the following interface command: service-module t1 lbo -7....
GRE tunnels are usually used in combination with a dynamic routing protocol that keeps the tunnel up and active. If you are using static routes there is no traffic to keep the tunnels up when the applications are not transmitting. You have two option...
If you a looking for acknowledgements from the receiver us can use snmp "informs" which are supported in most new versions of IOS.http://searchsystemsmanagement.techtarget.com/tip/1,289483,sid20_gci832132,00.html
