By internal memory, do you mean the internal SD card, or the flash internal to the unit? If the latter, you won't be able to save much, because the maps are large and the installed memory is comparatively small. You can still use the method above, but use /home/user/whatever instead of /media/mmc2, where 'whatever' is a folder in your user directory. You could also use just /home/user. With SD cards being so cheap, I have no idea why you would want to do that, but it's possible to get some in there, depending on what else you have installed.