Standing at the origin point of all spits, eggs, and husks (the exact center of the wurm) and using invulnerability skills to "body block" so nothing can get out. This is not the same as blocking with skills or Aegis, it must be invulnerability.
This requires good timing, positioning and skill along with keeping track of some cooldowns.
How to tell what you're blocking:
You may see "Invulnerable!" appear on your character. If you see a set of 3, you blocked eggs. If you see only a single message, you may have blocked a husk. Other attacks (eg. vet wurms) can trigger this message so it is not always reliable.
Set up one of your tabs in your chatbox so that Combat is selected, with Incoming Mitigated Damage checked off in the submenu. Things you successfully block are written in the log as "absorbed."
The attacks you want to see absorbed are "Spit" (eggs), "Disgorge Husk" (husks), and "Drool" (spit from small spins).
If there are multiple blockers at your wurm only one blocker will receive the message. Some blockers will type in chat if they are getting the invulns but if they do not you will have to block all double spits to be sure.
Skills: All the signets! Specifically, Midnight for an instant cast, and Illusions to recharge your shatters. More signets = more invulns. Feedback if you choose to use it as your primary reflect.
Traits (Trindine's build): Domination 2-2-2, Inspiration 3-1-1, Chronomancer 2-2-3
Use Blurred Frenzy (Sword 2) to avoid large spins. You can also use Echo of Memory (Shield 4) and allow it to fully channel, then use Deja Vu (Shield 4 again) for phantasm summons.
On small spins, you can use any signet to block the spit. Time your casting so that you finish at the time you expect the orange circle to appear.
For a double spit, use Distortion (F4). If you block eggs or are unsure, cast Signet of Illusions and use Distortion again on the next spit. Your traits should allow you to have enough illusions up for the full Distortion time.
If you mistime or don't have 3 illusions to shatter, you can use your signets for extra invulnerability.
Use your reflect skill of choice (Feedback or Focus 4) when you are certain of eggs.
Your invulns will be shared to nearby allies so they may end up blocking if you are slightly off position.
Replace your phantasms as necessary while waiting between animations. A clone can be summoned with Sword 3 if needed.
Skills: Conjure Earth Shield, Mist Form, other defensive skills of your choosing (eg. Arcane Shield)
Traits: Earth 1-3-3, Water 1-1-2, any other line (eg. Tempest 1-3-3)
Earth Shield 2 is a regular block (not invuln) that can be used on some spins.
It is difficult to block every single small spin along with the egg and husk spits. Be prepared to let some out to save your skills for the more important things.
Blocking skills: Fortify (Earth Shield 5), Obsidian Flesh (Focus - Earth 5), Mist Form, Take Root (Sylvari racial elite)
Reflects for guaranteed eggs: Swirling Winds (Focus - Air 4), or Magnetic Wave (Focus - Earth 4) with Ring of Earth (Dagger - Earth 2)
Obsidian Flesh is your longest duration block and the easiest to cover a full spit with. Chaining other skills together may be helpful to ensure you block all 3 waves.
Mist Form is the best skill to use to block selected small spins, like when the zerg is doing a crucial burn mechanic.