IMD files are excessively huge

Hi all
Firstly, my apologies if I've posted to the wrong forum section...
 
At work we use Caseware IDEA (v11.1 if it matters) to analyse large datasets, but something I've noticed is that the output files (saved as *.IMD) end up being colossal in size. I've opened some smaller ones in a text editor and I see a massive amount of references to "NULL" in the values, which I'm assuming is an empty value in the databases that were imported.
In some datasets we end up with over 300GB of "NULL" in a single file and this is making our space management a nightmare. I've tried compressing these files with apps like WinRAR and it can get sizes down from 300GB to 1.5GB so I'm confident that's exactly whats taking the space.
My question is, can IDEA be configured to store a literal empty space for empty values, instead of writing "NULL" on every single empty cell? This will free up more than 99% of my space issues with IDEA, and presumably make it work much faster since there's less data to read/write...