I don't know of a system that has been approved for the '44 (and I supect that Frank has never authorised one, so this will have to be an in country civil aviation authorisation) but the principle is the same as "in seat cargo" that has been used in the fixed wing world for many years.
What you need is a bag that "looks" as though it is nine g strong with loops to take the shoulder and lap straps. It should fit onto the seat looking like an overweight pax with no legs. Then get your local friendly Authority Airworthiness rep to have a look at your system.
If it looks sensible they will probably allow it on some kind of local agreement. It is highly unlikely that they will require a crash test of your machine with the bag in place, unless you operate in certain countries of which we all know...
The ones I remember years ago in airline work were heavy canvas like a mail bag, but cut in a pear shape. The volume was surprisingly large, and you had to be careful to check the mass of the stuff in it.
Try giving your CASA rep a call. Most of them are remarkably approachable on such subjects, and although they cannot legally suggest a solution, they will often give you a good idea of what might be approved if you presented it to them.
FWIW