Ok, things have completely changed. These are proprietary 5.8Ghz point-to-point links that connect several remote offices. Any ideas how to go about testing something like this!?

There was a presentation, maybe at Defcon, a year or so ago.  It explained how to unlock certain wireless cards to be able to listen on frequencies outside of the supported manufacturer's ranges.   Obviously there are issues with bricking and FCC, but it could be worth investigating.   

I am not an expert on this, but I think that 802.11a is the closest thing to that spectrum that is readily available.  I think 802.11a operates at 5.75 and 5.85 GHz ranges.   I am not sure if you can match the frequency of the point to point connections, but it's worth a shot. 

I don't know if this is within your scope though.  Unless your point to point connections are using 802.11a or 802.11n, I don't know what hacking your wireless card would prove.  This may be a shortcut, but my approach to these types of proprietary networks is usually to go over the AP and antennae settings to make sure properly authentication, encryption, etc are used.

Again, I am not a wireless expert, but these are my two cents.