gEDA-user: clearing mask

[Dave N6NZ]

Is there a way to clear an area of solder mask other then defining a 
ginormous pad and placing it?  I've got one of those parts that uses the 
PCB ground plane as heat sink.  I think I've got a footprint that will 
work nicely. It would be convenient if I could create a mask clearing 
polygon on the solder side that would expose whatever ground plane area 
is available for that.

-dave