Honestly, I don't view summoning as forcing an entity to be there against its own will. If they truly don't want to show up, they're not going to. I would also like to point out that Loki is more than a God of Trickery. He is hailed as the speaker of harsh truths, for one example.
Honestly, just look up things that Loki likes and then use them when you're trying to get his attention via an offering. He's one of the fire giants by blood, so burning an offering would be appropriate and simple.