You can install it just fine through GarnetVM, no hotsync needed.

1: Download metropalm.zip from the link in the OP's posting (or use http://download.nanika.net/metropalm.zip)

2: While you're at it, download MetrUp at the same time (through the link above, or directly: http://download.nanika.net/metrup.zip)

3: Unpack the zip file(s) somewhere.

4: Pick your version, e.g. metro-en.prc (for the English version)

5: Pick your towns/tubes/ from the selection of .pdb files (e.g. all/London-tourist.pdb)

6: Put your prc file(s) and your pdb file(s) on an SD card and install them one by one with the 'install' command in the Garnet VM interface.

7: When you start Metro from GarnetVM you'll see the towns/routes you loaded (as .pdb files) above.

8: Use MetrUp to get newer versions of the routes through the internet. It should also be able to automatically upgrade your metro version so that you don't need to re-install as newer versions become available, but as the version I installed is already the latest I haven't tested this. But it connects and checks ok at least.

(edit: speling tpyo fxide)