On my boom, I'm attaching the three blocks (two for mainsheet, one for vang) using simple loops. I simply make these by cutting a length of dyneema, then passing the two ends into the rope, while it's attached to the boom. it's extremely simple. With long tapered ends it's very secure under tension, and some lock-stitching (using waxed dyneema thread) holds it neatly while it's not under tension.
Here's a view while working: