Another idea.. sort of.

I do not think it is likely that two buttons will be pressed at the same time. So if the buttons are on the same port then read the port twice to see if the second one has been pushed.

Untested but something like
Code:
CHECK_BUTS:
BUTVAR = PORTB & $1F 
IF BUTVAR >= 1 THEN CHECK2
GOTO CHECK_BUTS

CHECK2
PAUSE 50
BUTVAR = PORTB & $1F
SELECT CASE BUTVAR
'insert case statements
GOTO CHECK_BUTS