Optimized is too small a term. It's neigh on impossible to responsibly load a plane without the required infrastructure in place, weight, balance, shifting loads and so on are all reasons why standardized cargo containers are used. Loose loads in aircraft can have this kind of effect:
So, assuming you can get the load safely in to the plane, without some kind of containerization inside it you are running a significant risk. Note that the video shows a crash due to one or more Humvees not being properly secured and I'd expect shifting loads to be a bit nicer than that on average but still, that's a risk that need not be taken.
Presumably something could be devised that bolts to the now-empty seat rails and provides a way to secure small cargo. It's entirely possible such a solution wouldn't be cost-effective, though.
Not for most commercial planes, no. Slightly off topic, as the number of planes is very small, but I have seen Russian load masters of old Russian military cargo planes applying some, let's say creative, ways of loose loading them.
I still prefer the properly controlled and planned way, so.
https://www.youtube.com/watch?v=p_eP0zdfZFk
So, assuming you can get the load safely in to the plane, without some kind of containerization inside it you are running a significant risk. Note that the video shows a crash due to one or more Humvees not being properly secured and I'd expect shifting loads to be a bit nicer than that on average but still, that's a risk that need not be taken.
Cargo planes are cargo planes for a reason.