I know this is an old thread but it helped me, so thanks! What i've done to get around this is use a double throw switch and connected it to my expansion card jumpers (used old 2 pin IDC connectors from PC LEDs), so when the switch is off it open a jumper that disables the first 4Mb of the 8 on the board, and it shorts a pin to say PCMCIA is used. The opposite happens when switched the other way. ie. the first 4Mb is renabled (jumper shorted), and the PCMCIA jumper is open circuit.
Obviously you can only do this if your expansion has similar jumpers to configure it, and only switch when its powered down.
I've mounted the switch under the floppy, in the expansion plate (the one that clips out), next to the other switch I mounted there for HDD selection (1, none, or 2).
