The WebViewer will show you map (nice), however there is no simple way to plot GPS location pins.
Open the browser to a Web page
Use these activity starter properties to open a specific web page:Action: android.intent.action.VIEW
DataUri: http://news.google.com
Where your link is substituted for ..news.google... does not work at all. Possibly because your link is a secure page.
The simple answer is you can not have the map and plot to it directly with the GPS receiver in a device. If you know the coordinates of the two alternate corners of your custom map, you could capture the image, place it into a Canvas, scale the Canvas to World location coordinates, and then plot the GPS points on the Canvas using 'Screen' coordinates where y maps to latitude and x to longitude.
A possible alternative is to use the Map possible in a fusion table as a display and post pins on it. That too could work for you but you would have a plain vanilla Google Map in the background.
Regards,
Steve