(Just happen to be surfing when you posted..heh)
It depends on the driver as to what the config.sys lines should be. The best advice I can give is RTM

If the driver doesn't support a switch to chose the com port (Something like /c 2, or /port com2...whatever), you'll have to find a driver that does.
Another tip, always load your drivers with DEVICEHIGH=, not DEVICE=, you'll save yourself some conventional memory that way.
<Reflects back on the old days of attempting to get Duke Nukem to run on a DOS 6.0 486dx2 66>