[Serusers] Multiple backup routes

Hi, if in a system i need to have more that one PSTN gateway to try for a destination in sequential order (note that gateways are dinamyc and may change call by call) and the order is important because them can be ordered for costs of the call from the less cost to the higher. There is a way for example to append all of them as branch and try them in sequence?? Otherwise i have to process them in a separate route block and have a temporary table in a database where take next gateways to try for that destination and that specific call, removing every cycle the used gateway. Any ideas to accomplish it in one step and let SER manage it?? Thanks, Bye, Marcello