Try this :

void LED_flash(void) interrupt 0 using 2
{
//bla bla bla :-)
}

The interrupt number causes a vector to be generated at (8*n+3),
where n is the argument of the "interrupt" declaration. Here a "LJMP LED_flash" will be placed at location 03h in the code memory.

EXT0 = 03h -> interrupt 0
EXT1 = 13h -> interrupt 2

Mathias