Yes there is a way. I assume that you have maps DVD version 10.1, correct?
All you need to "obtain" a file from 5.1 map's DVD - so called "loader.kwi"
Step 1: create an ISO file of your 10.1 DVD
Step 2: replace loader.kwi in that ISO file with 5.1 version of same file
Step 3: get a high quality DOUBLE layer blank DVD+R (8.5GB)
Step 4: use ImageBurn or other software of choice and burn the ISO as a DVD. YOU MUST MAKE SURE IT IS SET TO BOOKTYPE in order for Highlander to recognize it
Step 5: assuming that there is no map DVD in you HL, unplug the car battery for 5-10 min. Don't worry, the skies will not fall
Step 6: plug the battery back and load the new DVD. This will force 5.1 firmware/loader to load on your car. If you do not unplug the battery, the 10.1 firmware/loader will block the override
Step 7: follow easy steps to override the system AFTER you started the engine.
Note that the override is working with 10.1 maps only once; if you turn off the engine and start it again, you will need to do the override again
There is also a relevant thread here:
Override for Navi - v5.1 LOADING.KWI File
Linear Mode
