I don't use the Builder but I added a blank basemap directly to the config.xml to make this happen. All you have to do is add:
<layer label="Blank" type="dynamic" visible="false" url="" />
between the <basemaps> tags.
For 3.x, you can add a icon property pointing to a white/blank png file.
<layer label="Blank" type="dynamic" visible="false" icon="assets/images/basemap_blank.png" url="" />
I have little experience to play with the code, Trevor. By the way, my Flex is 3.1.
Try downloading a program called Notepad++, and use that program to edit your config.xml, as well as you widget .xml's.
addarcgisbasemaps="true"inside the <map> element.
<basemaps> <layer label="Aerial" type="tiled" visible="false" alpha="1" url="http://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer" icon="assets/images/basemap_imagery.jpg" /> <layer label="Topo" type="tiled" visible="false" alpha="1" url="http://server.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer" icon="assets/images/basemap_topographic.jpg" /> <layer label="Blank" type="dynamic" visible="false" url="" /> </basemaps>
The geometry service doesn't relate to the basemaps like that.
The basemaps are denoted in one of two ways.
Either using this:addarcgisbasemaps="true"inside the <map> element.
Or, adding each basemap you want individually like this inside the <map> element:
<basemaps> <layer label="Aerial" type="tiled" visible="false" alpha="1" url="http://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer" icon="assets/images/basemap_imagery.jpg" /> <layer label="Topo" type="tiled" visible="false" alpha="1" url="http://server.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer" icon="assets/images/basemap_topographic.jpg" /> <layer label="Blank" type="dynamic" visible="false" url="" /> </basemaps>