Well, the good news is that it has worked rather well! Using the IP check with DFP we targeted anyone within the beds.ac.uk domain. This has reaped some interesting results:
Up to a 1.1% CTR on internal banners which has been great for promotion of our internal services!
Below is a screenshot of the external site as seen by an internal viewer:
If you compare this to the live external site (beds.ac.uk) then you can see that the messaging is very different!
The only outstanding question now is how much more can we do with the system, text snippets that are changed on IP or country details would work or maybe looking at the idea of selling some spare impressions off...?