(adsbygoogle = window.adsbygoogle || []).push({}); If you have Dragon Born DLC, after reading one of the Black Books, you have the option to gain a power called "Secret of Arcana". Grab this power, and you can kill an enemy, activate this power, and continuously cast soul trap on the body for 30 seconds. When it runs out, wait 24 hours, and repeat.

You can cast soul trap on any low level dead enemy and it'll work just as well.

I believe the same goes for muffle (Illusion), and stoneflesh (Alteration), both easily brought up to 100 if spammed.