I did this in The Sahara
Have you tried the Abis over sat feature
Abis Over Sat Feature description :
This feature offers satellite transmission on the interface between the BTS and the BSC (the Abis interface). Using satellite transmission gives about 250 ms delays due to the long distances. The GSM standard specifies shorter delays. Longer delays leads to interruptions of the LAPD link. This feature will allow for a longer delays while maintaining the synchronisation on the transmission link.