It's very possible, you would need to go into the button handling code and switch around the two hold switch position ADC readings. It should be easy, unless I'm understanding something wrong here.
EDIT: A quick look through the sansa's button code confused me, the hold didn't work like I thought it did from what I saw.
EDIT2: Actually, it looks pretty easy. On line 250 of firmware\target\arm\/sandisk/sansa-e200/button-e200.c change
hold_button = (state & 0x80) != 0;
to whatever value is read when hold is off. At least I think that would be it.