For anyone planning a recce of the Volcano marathon route, here is a way-point file showing the cross-country part of the route.
The most tricky bit is the turn off from the Kau Desert Trail onto the Mauna Iki trail, but there are a number of spots where it is easy to mistake natural features for cairns.
The file is in gpx format. You can import this into google-earth to view it. Google earth should also install an application “gpsbabel” that can convert this into many other formats for importing to your gps device. Let me (email@example.com) know if you have problems.