How to make a non-interruptible port interruptible...

Hello!

The Details:

CC430F6137, custom hardware (extremely low power 5-400uA), CCS, USB FET

Background:

I made a boo-boo in my hardware design and now realize now that I need to make the I/O on port 5.4 "interruptible" somehow.  I know this isn't directly possible however I believe there are alternate solutions.  I considered:

1. (Dumb as nails) input polling inside main() loop
   1. Pro: Easy to code
   2. Con: burdens the CPU with wasteful code
2. Using a comparator which triggers an ISR based on a ref of 1/2VCC. 
   1. Pro: Would work with little software control
   2. Con: Wouldn't need this module except for this function & consumption is relatively high for this module (40-65uA or 20% of my budget)
3. A timer with an ISR to pseudo-poll (instead of inside the main() loop)
   1. Pro: Simple, would work, low power, configurable latency (of registering IO state change)
   2. Con: the shorter the duration of the timer, less latency but higher CPU usage/current

Question(s):

Can I minimize software "up-time" to monitor this pin? Which of the above three options would you choose? Is there something more elegant you could suggest that I haven't considered?

Any thoughts would be great!  

Thank you!

MK