This will be made possible soon, but I haven't finished it yet.

Basically, it involves detecting when the last item of the set is equipped, and adding an additional bonus.
Once once of the items of the set is unequipped, that bonus should be removed.

That's the plan. It's quite a volatile activity though, because the engine does some serious calculations and multiple levels of caching to the items and player statistics.

Other games generally do a much less efficient thing and just enumerate all item stats on the fly. It means implementing sets is easier, but on the whole, it's bad. Round 3 did this terrible enumerating and it's one of the reasons I made round 4
I calculate the effects and cache them when they are equipped.

I know someone who is for this for  idea. Do it for JD!