Have a read of (I know you've done that but the references might be useful for other readers) -
(a)
CAO 20.16.1
(b)
CAO 20.16.2
(c)
CAO 20.16.3
(d)
CAO 100.7
Basically means that you should have some paperwork in your flight manual signed by a weight control officer which either says that your aeroplane can't be loaded outside the envelope or gives you details of the current approved loading system .. which, probably, isn't the desired electronic animal.
If you want to use an electronic gizmo, then you should engage a WCO to check that it complies with the Orders and call it up in the Flight Manual.
Alternatively, if your aeroplane has a simple set of load rules, you should be able to check that the electronic gadget keeps you inside the parameters of the load rules and, in effect, you are complying with the load rules.
Beyond the above it's a bit difficult to provide advice without having a looksee at the specific aircraft's paperwork.
The main problem with Excel is that you would need to have a lot of protections in the sheet for the WCO to sign off on it.