Naphtali
The shotgun load was stabilized with card wads, just as in a BP shotgun. I find it takes two to stabilize a load of BB's, I haven't tried to load 00 Buck or buy the Navy Arms mold that makes larger balls for it. Larger balls should be much easier to stabilize than BB's. Remember too that it can be loaded with a single round ball, patched. Again, the same as a musket or shotgun.
My problem with the LeMat is that the rammer retaining spring is inadequate. I've e-mailed Pietta and had discussions with Mr. Pietta about this, have installed another spring, and still the loading lever comes loose by the fourth or fifth shot. I think the geometry of the spring is slightly off.
Sorry, I don't know anyone who is modifying this arm. If it is historically accurate and you have sources with diagrams or an example, why not contact Pietta? They may even be interested in manufacturing the modification. However you do it, don't expect it to be cheap.