Last year I couldn't find shiso so this year I grew some from seed. Now I have so much I want to save some for winter.

Shiso leaves are traditionally found with pickled ginger, so you could try using that technique. The recipe in Seductions of Rice (Alford and Duguid), p. 203, looks right. (I used www.eatyourbooks.com to find it on my own shelf, and, since they now index food52, found that there are recipes here using shiso -- worth a search.) You probably know that shiso is also (in English) called perilla.

Check this out http://www.justhungry.com/preserving-shiso-basil-lemon-verbena-and-other-herbs