I was looking for a similar solution, but with a DIR-300 as the second "booster" lizzi555 walked me through a perfect way to do it.

I hope he is cool that I pass this on!
Firstly, use a powerline setup to link the two units.
Come out of any LAN port of the first 655 into the first powerline unit
Go into one of the LAN ports (NOT the WAN) of the second unit from the second powerline unit.
Disable DHCP server on the second 655
Set all units to fixed channels, that do not interfere, or clash with other WLAN networks around you - for instance, first 655 to Channel 1, extension channel 5, (If you are using N), and the second 655 to channel 11 or higher.
Set the second 655 to the same LAN IP as the first 655.
Assign a different SSID to the second 655.
Secure the second 655 with the same level of encryption as your first, (But it does not have to be the same password, as it is a separate SSID)
Then you can access everything on your network by signing onto the appropriate SSID!
It is perfect - but someone please correct me if I miss something out - it works great for me, though!
Again, thanks to lizzi555 for this fix!