You can edit /etc/rc.conf file using vi text editor:
Append following line to file
Code:
ifconfig_lnc0_alias0="192.168.1.5 netmask 255.255.255.255"
Replace lnc0 and ip with your own ip, make sure you use 255.255.255.255 as subnet (other than actual subnet)
Restart network service:
Code:
/etc/rc.d/netif restart