[mkgmap-dev] routable tiles with visible seas

I've been following the "sea floods" topic and have found that ,yes, a x4b polygon is not needed to generate 'non flooding' seas. However, I 'm finding ,I need to include x4b at draworder=0 (sea at order 1 & land at 2) to override Mapsource's hideous basemap, It works brilliantly - all islands appear; no flooding, even in the most 'challenging' circumstances and no basemap! Unfortunately, those tiles are not routable as mkgmap --routes only seems to work with a default style. Is there any way of tweaking mkgmap? Many Thanks Nick