How to upgrade Cisco 675 with linux?

Hi,
Is there a way to get the CBOS 2.4.3 for a 675 and install it with Linux
via the terminal port and a com program. I have tried connecting via
modem serial port but I'm not really sure how to do the upgrade. I'm in
routing mode so I don't think I can use the tftp procedure as the router
doesn't have a IP address.

Any help appreciated,
Eric :-)

p.s. I hate to resort to another OS for this task.