No, you can't do that as far as I know. On the other hand, most chips with an ADC also have a comparator module which output CAN trip an interrupt. If the chip you're using got one then simply connect the analog signal to the ADC input and to the comparator input and set up a suitable trip level on the "other" comparator input - should do it.

Or, short of an on board comparator, use an external one and wire its output to RB0 - for example.