You can rig up connections to the appropriate isp pins on the cpu with whatever you have handy. Here is a schematic that has the isp mapping:
http://www.arduino.cc/en/uploads/Mai...-schematic.pdf
I made an "in circuit" adapter for my ftdi cable out of an extra DIP socket (plus hotglue and careful bending of the tips, reset cap, etc, etc). I just press it on while programming. Maybe rig something like this up if you plan on doing it more than once.
