1.) find the mac address of your phone (this can be found under advanced menu option within the system -> wifi settings (or alternatively under about phone)
2.) login to your dd-wrt control panel
3.) go to services
4.) under static leases click add and then enter the mac address of your phone, pick any host name and ip address you'd like, and leave lease time blank
5.) scroll down and click apply settings and then save
6.) go to administration
7.) go to commands
8.) enter the following:
arp -i br0 -s xxx.xxx.xxx.xxx xx:xx:xx:xx:xx:xx
obviously, you'll need to use the static ip you set in step 4 and the second string will be your phone's mac address
9.) scroll down and click save startup
10.) reboot your router
11.) reboot your phone
12.) you're done!
if you want to be sure the settings took, log back into your router control panel and go to administration -> commands and type "arp -a" minus the quotes, then click run commands. this will give you a list of all active clients in your arp table, and you should see your phone listed.
note: the only item within this list that i'm unsure about is whether or not the host name matters. i set my host name on my router control panel as "nexus4" whereas by default your phone will have a hostname of android-<serial-number>. just to be sure there were no issues, i used trickster to manually set my host name on my phone to nexus4. ymmv.