I use GPS tools for database hiking trails in Bosnia.

I know that there is no option of using OSM in the GPS Tools, but I found that there is a possibility of adding OSM layers over google maps on this link:
http://wiki.openstreetmap.org/wiki/Google_Maps_Example (Example - Using Google Maps API v3 setting OSM as a base map layer)

Can you tell me which files should be modified to add this layer?

Thanks in advance, 
Midhat