Get a mortar and pestle & use liquid nitrogen to chill them down before grinding your sample in liquid nitrogen. As long as the sample stays completely frozen the entire time, then you're just fine. Grind to a very, very fine powder (like makeup or flour). Add a tiny bit more liquid nitrogen and "swirl & pour" into a 1.7 ml tube (DO NOT CLOSE THE LID until the liquid nitrogen has all evaporated). Then put tube with powdered tissue in liquid nitrogen. Can either put in -80*C freezer or continue the extraction protocol.

The tissue can thaw only when you have added the first buffer from the extraction protocol.