Not sure which garmin you have and whether its removable from plane. If yes its really easy to transfer route from SD to Garmin; can even do it with an old Pilot 3 via usb/serial converter. 296 and upwards is via USB cable.Data transfer takes about 10 secs.
Need to remember that it does clog up your garmin with waypoints but these can be removed from time to time very easily (and by category).
Cheers
david