[SR-Users] Measuring subscriber latency

Hi all I'm replacing an Asterisk based system with a kamailio based one. One of the features the legacy system has is showing the subscriber the latency obtained from the qualify option of sip.conf Now, I'd like to measure the latency but I'm not sure how to do it. AFAIK nathelper module sends the OPTIONS keepalive messages stateless mode and there's no information there. I was thinking on triggering a route send_options via the timer module, save the timestamp of the relay and the timestamp of the response in onreply_route but it doesn't look elegant. Creating my own daemon in an external server and reading the info from the location module seems to be another option. I guess I'm not the first one with this need so I wonder if there's an already existing solution or an elegant way of dealing with it. any ideas? thanks, Jon