Its certainly possible to copy the file over via the network to the compact flash card in your Roku (so you don't need a pc compact flash reader/writer).
Now i just need that package to arrive then.
Just remember that by default the compact flash card is read-only, so you'll need to first execute the commands to make it read/write (a quick search should find the relevant commands).
Then copy the file over, reboot your machine, wait a few minutes and you should be updated.
Don't forget to remove the file from the compact flash card when you've updated, otherwise it will try to upgrade your machine every time you reboor (with the compact flash card in the Roku).