Arduino Mega Analog Comparator?

I was looking at the schematics for the Arduino Mega (and the more recent Mega2560), and it appears that AIN1 is connected to D5 and AIN0 is disconnected. This is different from the Uno/Duemilanove Arduinos which have AIN1 hooked to D7 and AIN0 hooked to D6.

I'm working on a shield which can hook up to both the Mega series and Uno/Duemilanove boards and uses the Arduino analog comparator (more specifically I want to use the rising/falling edge interrupts).

Is there an alternative interrupt solution? I'm using the ADC so switching the ADC clock off isn't a viable solution. I'm open to the potential of having to use an external comparator chip, but I really need the rising/falling external interrupt trigger.

For reference, the shield I'm working on is similar to the Girino Arduino Oscilloscope project.

I haven't looked at your harware, but do you really need both pins of the comparator?

It is possible to internally connected AIN0 to a 1.1V reference. Depending on you circuit, it might be possible to condition the signal going to AIN1 to trigger an interrupt when it rises above, or falls below 1.1v.

Failing that, you could use an external comparator as you say. In which case, setup the comparator to output 0v for low and 5v for high, then connect that to one of the external interrupt pins (Digital 2 or Digital 3).