I tried some once, but without any success. At the time, I didn't really look into
why they failed, but I suspect they required +12V and -12V which the webpal ISA
interfaces doesn't supply. If you could find a +5V only card, it would
probably work. Or you could wire up +12V and -12V to the appropriate pins
(watch out since the +12V pin is currently wired to the +5V line so be sure
to break that connection).
Note that the ISA bus IO addresses reside in a different address space from
the SuperIO chip so using an ISA bus I/O card wouldn't help in the
bootstrapping process since the internal code that comes with the webpal
outputs / reads from the SuperIO serial port, not one in the ISA bus
In theory, you could use a serial card to get access to another
serial port from Linux, but most people would rather have an ethernet
interface than another serial port.
My assumption is that you were interested in this to try and do the
bootstrapping process without having to build any hardware.