Increment Acct-Delay-Time on proxy

Hello, I've installed FreeRADIUS 2.1.7 on a CentOS system. In my setup, the RADIUS server will work as proxy, storing locally the accounting packets if the destination servers are down, and resending them when the destination servers are up again. To achieve this result I've followed the "robust-proxy-accounting" example config file with success. Now I'm looking for a way to update the "Acct-Delay-Time", so that, when the destination servers are back, the packet is read from the "detail" file and is sent by the proxy adding to the Acct-Delay-Time the delay introduced by the temporary failure at the proxy level. Is there a way to do this with FreeRADIUS? Thanks! Emanuele