the short answer is no..
long answer.. anything is possible with time and money. but you need a face plate, another entire layer for to drive bay assembly, another 4 caddies, the backplane, the backplane mounting clips X3, a bunch of really hard to source screws, and then umm .. yeah.. not to mention you need the assembly for the backplane you already have. they changed with the different model of backplanes. they might not have them if it is an older unit.
even if norco sold all of the parts individually, It would probably cost as much as a new chassis.
I guess you could always call their sales dept and ask if they could get you a "kit" to make the upgrade.
you might be able to mount 4 drives internal with minor modding so it is 20 swappable and 4 hard mounted...