To get round the fact that your devices aren't in a dns table you could use the host file feature in syslog. There is a static hosts file in the root of your syslog folder. Just add your devices ip and hostname into this file, restart your syslog service and away you go. This may not be the answer you are looking for but it works great for me.
ok, mapping IPs to hostnames in LAN.
but what about IPs in WAN?
Have I to change internet addresses to names internet names? :P