displaying nearshore wavewatch III data

[Amos Wright]

I'm using wavewatch III data in opengrads to visualize coastal
predictions. using "gxout shaded" produces beautiful images... but
they are understandably 'rough edged' at the immediate coast; for
example swell data it is not extrapolated beyond the grid boxes with
defined values...

what i would like to know is if there is a setting [or trick!] to
extend the shading beyond the grid boxes with values, and then overlay
the map on top of it, so that the [swell] data appear to extend
directly to the coast.

Thank you much,
Sincerely,
Amos