Just uploaded this last night.
In the spiderguard the idea is to stretch your opponent out by pulling with your arms (mostly) and pushing with your feet (mostly) so that he feels like a scarecrow, is unable to launch an effective guard pass, and also is much more susceptible to your attacks (especially the omoplata and triangle choke).
But controlling the wrists is tricky in nogi unless you're a Nogueira-like mutant with killer killer grip.
Here's how to apply the same push-pull principle in nogi to set up a sweet little triangle choke