The reprap hosts does this by default. I think it can also be turned on and off and the location of the dump can be modified in the preferences.
With Skeinforge 40, you can do this with a start.gcode file in your alterations folder. It can contain something like this:
... other stuff
G1 Z10.0 F60.0
G1 X130.0 Y0.0 F3000.0
G92 E0
G1 F30.0
G1 E10.0 F30.0
G1 E9.0 F720.0 ;retract 1 mm, change to your retract setting
G28 Z0
G28 X0 Y0
...more stuff
