You can import custom KML POI's with a Magellan's Content Manager software.
How to import custom KML files to the Magellan:
1. Connect your Magellan to your computer.
2. Open Content Manager.
3. Click on the "Tools" --> "Transfer Trip Plans" to open "Manage Trip Plans".
4. Click on a "Import as POI" button.
5. Find any KML or KMZ file on your computer
6. Click on the "Open" button.
A box will open to tell you whether or not the import was successful.