Would it be possible to add an option to have this :
gmt begin test png
gmt basemap -R-1/1/-1/1 -JX10c -Bafg --MAP_FRAME_PEN=0p
gmt basemap -Bb --MAP_FRAME_TYPE=graph -Y5c
gmt basemap -Bl --MAP_FRAME_TYPE=graph -Y-5c -X5c
gmt end show

By parsing this simple parameter :
gmt basemap -R-1/1/-1/1 -JX10c -Bafg --MAP_FRAME_TYPE=graph,centered -png result
Best,
Guillaume
cf forum