Are they frozen bloodworms?
Soaking in garlic juice is a good first effort, garlic makes everything tasty! ;)
If they are frozen bloodworms; I have no idea if this will work, I only just thought of it now.
I thaw frozen bloodworms in a bit of tank water in a cup. There is always some amount of "goo" I'll call it, from the bloodworms. Well basically just red tinged water. I'm wondering, if you soak the pellets in that water, which hypothetically should have some sort of bloodworm flavored goodness...that this will trick him into eating the pellets? And if it works...trying that for a few days maybe you can wean him onto pellets soaked in just tank water, and then after that just drop the pellets in and see what happens.