[Wlug] DHCPCD and ADSL modem

Hello, I have a ADSL modem. This modem containa DHCP server that I use. In my computer, I have dhcp client daemon (dhcpcd). The parameter of dhcp server is juste lease-time and IP adresse, but I would like to set a name of my computer and kown the name and IP adresse of other computer. If I configure a DDNS for make it, it's not a problem. How-to configure a DDNS updatefrom a dhcp server not configurable ? Thanks !