If you take apart a blink(1), you’ll see it has three tiny plated holes. These are the three needed by WS2812 LEDs: +5V, Gnd, and Data.
Or, in diagram form against a standard WS2812B strip:
Taking apart a blink(1) to wire it up for extra LEDs isn’t too difficult if you’re okay with a bit of soldering. Here’s videos showing two different ways to do it: