consdev ucom0 ?

I'd like to use a serial console with a Dell OptiPlex 7440 PC to
capture the output when it fails to boot, but the PC doesn't have a
serial port, at least not externally.  I wonder if it's somehow
possible to use the consdev boot command to direct the serial I/O to
pass through a Belkin USB to RS-232 adapter instead of a conventional
com port.  The install kernel recognises the adapter (although these
lines are from when it was plugged into an OptiPlex 990):

umct0 at uhub2 port 4
umct0: Belkin USB PDA Adapter Belkin Components, rev 1.10/1.02, addr 4
ucom0 at umct0


Ray