The GNS 480 and the MX 20 use a standard windows CF
reader (which they give you a sandisk one with the units).
The cards have a serial number hidden in one of the FS
fields, but otherwise are standard. JSUM pretty
much doesn't care what hardware device you use to program
it as it uses the standard windows filesystem calls to
access it.

I've used a PCCARD-CF adapater to program mine.