face alpha for range of raster values

Hello,

I'm plotting raster data with the mapshow function and would like to set the raster values that are NaN to completely transparent, and the rest to partially transparent. The below sample code creates an example raster file with NaN values. Then it plot the data and sets the transparency of all the data, but I can't figure out how to set the transparency of just the NaN values.

Z = peaks(140);
Z(81:end,:) = [];
Z(Z < 0.5 & Z > -0.5)= nan;
R = maprasterref('RasterSize',[80 140],'ColumnsStartFrom','north','XLimWorld',[1345084 1437484],'YLimWorld',[369602 422402]);
key.GTModelTypeGeoKey = 1;
key.GTRasterTypeGeoKey = 1;
key.ProjectedCSTypeGeoKey = 32104;
geotiffwrite('testraster',Z,R,'GeoKeyDirectoryTag',key)
t = mapshow('testraster.tif','DisplayType','texture');
t.FaceAlpha = 0.5;

Thanks for your time and wisdome!