Best way to level up Blood Magic?

I find it difficult to level up the blood magic skill. I am playing mostly as a Shield Bot for my group (I enjoy it!) but that doesn't leave a lot of room to level up that skill. So I want a mostly AFK way to farm exp.

I have read the advice from the wiki, but I can't seem to successfully make a spawner-based farm, the spawner always gets broken. The Elder and Bonemass are both too scary for me, I wouldn't afk with them. I tried the Elder, but I need to pay attention to him, and I assume Bonemass will be the same.

Right now I am thinking of digging a pit, summon a Troll and have 4 archers shoot at it? Would that be effective? Or does someone have a better way to level up?

Also, secondary question, I don't see the Staff of Fracturing and Dundr as useful.... is there a reason to use them at all?