masked continents on polar stereographic map with circular frame?

[Michael Sigmond]

Hello,
I'm trying to plot a variable on a polar stereographic map, filling the the
continents with a gray color, and with a circular frame (I know, that's a
lot to ask..)

I'm using:

set mproj sps
set lat -90 -50
set mpvals -180 180 -90 -50
set frame circle
d variable

I tried using basemap, but then the frame turns square, which I don't really
like. Any suggestions are much appreciated!

Thank you,

Michael