There has to be an easier way. I'm assuming portb.0 is held high with a pullup. Try something like this:

START:
IF PORTB.0 = 0 THEN TOGGLE PORTB.1 : GOTO WAITFORRELEASE
GOTO START

WAITFORRELEASE:
PAUSE 50
IF PORTB.0 = 0 THEN WAITFORRELEASE
GOTO START