Not realy enough information to go on since you didn't state what type of GPS
system. It all depends on if the GPS system can be configured either through
an import mechanism, configuration files, and so on.
You're going to have to dig a little for information on the GPS system. Start
with the Manufacturer and ask them directly, google the product and see what
others have done, etc. Assuming it's not a closed system, you may even be able
to open up some of the configuration files to see how waypoints/push
pins/markers are stored.